diff --git a/accessible/base/moz.build b/accessible/base/moz.build
index 0a86a98a3d29..9fe296fc8368 100644
--- a/accessible/base/moz.build
+++ b/accessible/base/moz.build
@@ -114,3 +114,6 @@ include('/ipc/chromium/chromium-config.mozbuild')
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/accessible/generic/moz.build b/accessible/generic/moz.build
index a2a0090d0334..6a3783550e71 100644
--- a/accessible/generic/moz.build
+++ b/accessible/generic/moz.build
@@ -70,3 +70,6 @@ include('/ipc/chromium/chromium-config.mozbuild')
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/accessible/interfaces/ia2/moz.build b/accessible/interfaces/ia2/moz.build
index da3d1d39b058..5ba924822d5e 100644
--- a/accessible/interfaces/ia2/moz.build
+++ b/accessible/interfaces/ia2/moz.build
@@ -98,3 +98,6 @@ if CONFIG['CC_TYPE'] == 'clang-cl':
         '-Wno-missing-braces',
         '-Wno-unused-const-variable',
     ]
+
+if CONFIG['MOZ_PGO'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/accessible/interfaces/msaa/moz.build b/accessible/interfaces/msaa/moz.build
index 14aabb852e2f..2eb59bff56ce 100644
--- a/accessible/interfaces/msaa/moz.build
+++ b/accessible/interfaces/msaa/moz.build
@@ -44,3 +44,6 @@ if CONFIG['CC_TYPE'] == 'clang-cl':
         '-Wno-missing-braces',
         '-Wno-unused-const-variable',
     ]
+
+if CONFIG['MOZ_PGO'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/accessible/ipc/moz.build b/accessible/ipc/moz.build
index 96d7de6b7cae..b47a25356a8b 100644
--- a/accessible/ipc/moz.build
+++ b/accessible/ipc/moz.build
@@ -62,3 +62,6 @@ FINAL_LIBRARY = 'xul'
 
 # Add libFuzzer configuration directives
 include('/tools/fuzzing/libfuzzer-config.mozbuild')
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/accessible/ipc/win/handler/moz.build b/accessible/ipc/win/handler/moz.build
index 0e2be334b871..fae401fef0b5 100644
--- a/accessible/ipc/win/handler/moz.build
+++ b/accessible/ipc/win/handler/moz.build
@@ -83,3 +83,5 @@ LIBRARY_DEFINES['_UNICODE'] = True
 LIBRARY_DEFINES['MOZ_NO_MOZALLOC'] = True
 DisableStlWrapping()
 
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/accessible/ipc/win/moz.build b/accessible/ipc/win/moz.build
index 10e91842c5a8..aa37dce7f360 100644
--- a/accessible/ipc/win/moz.build
+++ b/accessible/ipc/win/moz.build
@@ -55,3 +55,6 @@ if CONFIG['ACCESSIBILITY']:
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/accessible/windows/msaa/moz.build b/accessible/windows/msaa/moz.build
index 499df9db21a5..34cf22bbd9d8 100644
--- a/accessible/windows/msaa/moz.build
+++ b/accessible/windows/msaa/moz.build
@@ -84,3 +84,6 @@ if CONFIG['CC_TYPE'] == 'clang-cl':
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/accessible/windows/sdn/moz.build b/accessible/windows/sdn/moz.build
index ae0d5e20dcb0..c879e320e6f1 100644
--- a/accessible/windows/sdn/moz.build
+++ b/accessible/windows/sdn/moz.build
@@ -22,3 +22,6 @@ LOCAL_INCLUDES += [
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/accessible/xpcom/moz.build b/accessible/xpcom/moz.build
index 7bd432003dd6..aa7a2b55a95e 100644
--- a/accessible/xpcom/moz.build
+++ b/accessible/xpcom/moz.build
@@ -64,3 +64,6 @@ include('/ipc/chromium/chromium-config.mozbuild')
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/browser/app/winlauncher/moz.build b/browser/app/winlauncher/moz.build
index c286b3120c8d..c260588cb4e9 100644
--- a/browser/app/winlauncher/moz.build
+++ b/browser/app/winlauncher/moz.build
@@ -25,3 +25,6 @@ TEST_DIRS += [
 ]
 
 DisableStlWrapping()
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/browser/app/winlauncher/test/moz.build b/browser/app/winlauncher/test/moz.build
index 31fbe296eeb2..2208aa5e3c06 100644
--- a/browser/app/winlauncher/test/moz.build
+++ b/browser/app/winlauncher/test/moz.build
@@ -15,3 +15,6 @@ LOCAL_INCLUDES += [
 OS_LIBS += [
     'ntdll',
 ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/build/clang-plugin/tests/moz.build b/build/clang-plugin/tests/moz.build
index 873b8f15cce0..2d76d22498e2 100644
--- a/build/clang-plugin/tests/moz.build
+++ b/build/clang-plugin/tests/moz.build
@@ -66,3 +66,6 @@ COMPILE_FLAGS['OS_CFLAGS'] = (
     ['-fsyntax-only', '-Xclang', '-verify', '-ferror-limit=0', '-std=c11',
      '-Wno-invalid-noreturn']
 )
+
+if CONFIG['ENABLE_CLANG_PLUGIN'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/build/win32/moz.build b/build/win32/moz.build
index 1f0fc2a5e55a..21df3e5c0ed6 100644
--- a/build/win32/moz.build
+++ b/build/win32/moz.build
@@ -32,3 +32,6 @@ if CONFIG['LLVM_SYMBOLIZER'] and CONFIG['WIN_DIA_SDK_BIN_DIR']:
     FINAL_TARGET_FILES += [
         '%%%s/msdia140.dll' % CONFIG['WIN_DIA_SDK_BIN_DIR']
     ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/base/moz.build b/dom/base/moz.build
index aadffb390984..c7e93499e22e 100644
--- a/dom/base/moz.build
+++ b/dom/base/moz.build
@@ -510,3 +510,6 @@ counterlist.inputs = ['UseCounters.conf']
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/encoding/moz.build b/dom/encoding/moz.build
index 63be7903e736..537b00b32e1b 100644
--- a/dom/encoding/moz.build
+++ b/dom/encoding/moz.build
@@ -51,3 +51,7 @@ MOCHITEST_MANIFESTS += [
 ]
 MOCHITEST_CHROME_MANIFESTS += ['test/chrome.ini']
 XPCSHELL_TESTS_MANIFESTS += ['test/unit/xpcshell.ini']
+
+if (not CONFIG['HAVE_64BIT_BUILD'] and
+    CONFIG['ENABLE_CLANG_PLUGIN'] and CONFIG['CC_TYPE'] == 'clang-cl'):
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/indexedDB/moz.build b/dom/indexedDB/moz.build
index 4549066510f2..9e5676e1de50 100644
--- a/dom/indexedDB/moz.build
+++ b/dom/indexedDB/moz.build
@@ -115,3 +115,7 @@ XPIDL_SOURCES += [
 ]
 
 XPIDL_MODULE = 'dom_indexeddb'
+
+if (not CONFIG['HAVE_64BIT_BUILD'] and
+    CONFIG['ENABLE_CLANG_PLUGIN'] and CONFIG['CC_TYPE'] == 'clang-cl'):
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/media/fake-cdm/moz.build b/dom/media/fake-cdm/moz.build
index ef54e912958f..76c56758312d 100644
--- a/dom/media/fake-cdm/moz.build
+++ b/dom/media/fake-cdm/moz.build
@@ -30,3 +30,6 @@ NoVisibilityFlags()
 # Don't use STL wrappers; this isn't Gecko code
 DisableStlWrapping()
 NO_PGO = True
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/media/gmp/moz.build b/dom/media/gmp/moz.build
index 7e52adde7b54..ca0f56db0901 100644
--- a/dom/media/gmp/moz.build
+++ b/dom/media/gmp/moz.build
@@ -148,3 +148,6 @@ LOCAL_INCLUDES += [
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/media/gtest/moz.build b/dom/media/gtest/moz.build
index 781ffa519eb7..7764a080ee62 100644
--- a/dom/media/gtest/moz.build
+++ b/dom/media/gtest/moz.build
@@ -88,3 +88,6 @@ FINAL_LIBRARY = 'xul-gtest'
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow', '-Wno-unused-private-field']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/media/webrtc/moz.build b/dom/media/webrtc/moz.build
index 75e4625ba8b4..71fd92f2eba6 100644
--- a/dom/media/webrtc/moz.build
+++ b/dom/media/webrtc/moz.build
@@ -88,3 +88,6 @@ if CONFIG['CC_TYPE'] in ('msvc', 'clang-cl'):
                    # 'reinterpret_cast': conversion from 'DWORD' to 'HANDLE' of greater size
     ]
     DEFINES['__PRETTY_FUNCTION__'] = '__FUNCSIG__'
+
+if CONFIG['MOZ_ASAN'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1306642
diff --git a/dom/plugins/base/moz.build b/dom/plugins/base/moz.build
index 7f6161d80a51..57027479efee 100644
--- a/dom/plugins/base/moz.build
+++ b/dom/plugins/base/moz.build
@@ -92,3 +92,6 @@ CXXFLAGS += CONFIG['TK_CFLAGS']
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/plugins/ipc/hangui/moz.build b/dom/plugins/ipc/hangui/moz.build
index 213ead658e7a..bf6583ea3c44 100644
--- a/dom/plugins/ipc/hangui/moz.build
+++ b/dom/plugins/ipc/hangui/moz.build
@@ -25,3 +25,8 @@ RCINCLUDE = 'HangUIDlg.rc'
 OS_LIBS += [
     'comctl32',
 ]
+
+if ((CONFIG['MOZ_PGO'] or
+     (not CONFIG['HAVE_64BIT_BUILD'] and CONFIG['ENABLE_CLANG_PLUGIN']))
+    and CONFIG['CC_TYPE'] == 'clang-cl'):
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/plugins/ipc/moz.build b/dom/plugins/ipc/moz.build
index 52b2e00e65da..14ffb1da521c 100644
--- a/dom/plugins/ipc/moz.build
+++ b/dom/plugins/ipc/moz.build
@@ -155,3 +155,6 @@ if CONFIG['CC_TYPE'] in ('msvc', 'clang-cl'):
 
     # 'type cast': conversion from 'unsigned int' to 'HIMC' of greater size
     CXXFLAGS += ['-wd4312']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/plugins/test/testplugin/testplugin.mozbuild b/dom/plugins/test/testplugin/testplugin.mozbuild
index cf25ade37042..ef87fb6eb34a 100644
--- a/dom/plugins/test/testplugin/testplugin.mozbuild
+++ b/dom/plugins/test/testplugin/testplugin.mozbuild
@@ -68,3 +68,6 @@ else:
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/storage/moz.build b/dom/storage/moz.build
index 4003e44ff18c..b47f270adab8 100644
--- a/dom/storage/moz.build
+++ b/dom/storage/moz.build
@@ -49,3 +49,6 @@ LOCAL_INCLUDES += [
 
 if CONFIG['ENABLE_TESTS']:
     DEFINES['DOM_STORAGE_TESTS'] = True
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/dom/url/moz.build b/dom/url/moz.build
index 2c8545912907..45d33a449295 100644
--- a/dom/url/moz.build
+++ b/dom/url/moz.build
@@ -30,3 +30,6 @@ BROWSER_CHROME_MANIFESTS += [ 'tests/browser.ini' ]
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['MOZ_PGO'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/gfx/2d/moz.build b/gfx/2d/moz.build
index dfce6c7ba3e0..82456aba2b81 100644
--- a/gfx/2d/moz.build
+++ b/gfx/2d/moz.build
@@ -255,3 +255,5 @@ if CONFIG['MOZ_ENABLE_SKIA_GPU']:
         '/gfx/skia/skia/src/gpu',
     ]
 
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/gfx/gl/moz.build b/gfx/gl/moz.build
index b54f52c84c29..76799bb29f1a 100644
--- a/gfx/gl/moz.build
+++ b/gfx/gl/moz.build
@@ -166,3 +166,6 @@ LOCAL_INCLUDES += CONFIG['SKIA_INCLUDES']
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/gfx/layers/moz.build b/gfx/layers/moz.build
index 8d9acc5b8cd7..f0ebc6fa2dea 100755
--- a/gfx/layers/moz.build
+++ b/gfx/layers/moz.build
@@ -583,3 +583,6 @@ if CONFIG['MOZ_ENABLE_SKIA']:
   UNIFIED_SOURCES += [
     'composite/PaintCounter.cpp',
   ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/gfx/thebes/moz.build b/gfx/thebes/moz.build
index e29c26fd7dc6..0fcbfb78ea2a 100644
--- a/gfx/thebes/moz.build
+++ b/gfx/thebes/moz.build
@@ -293,3 +293,6 @@ DEFINES['GRAPHITE2_STATIC'] = True
 if CONFIG['CC_TYPE'] == 'clang':
     # Suppress warnings from Skia header files.
     SOURCES['gfxPlatform.cpp'].flags += ['-Wno-implicit-fallthrough']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/gfx/vr/moz.build b/gfx/vr/moz.build
index c9abde79a3f3..d66f9e2e91ea 100644
--- a/gfx/vr/moz.build
+++ b/gfx/vr/moz.build
@@ -97,3 +97,6 @@ if CONFIG['CC_TYPE'] in ('msvc', 'clang-cl'):
     # ovr_capi_dynamic.h '<unnamed-tag>': Alignment specifier is less than
     # actual alignment (8), and will be ignored
     CXXFLAGS += ['-wd4359']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/gfx/webrender_bindings/moz.build b/gfx/webrender_bindings/moz.build
index f2d34cd1fe3c..45439d62d38f 100644
--- a/gfx/webrender_bindings/moz.build
+++ b/gfx/webrender_bindings/moz.build
@@ -66,3 +66,6 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] in ('android', 'gtk3'):
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/ipc/chromium/moz.build b/ipc/chromium/moz.build
index 315f30bae5f7..193685738b32 100644
--- a/ipc/chromium/moz.build
+++ b/ipc/chromium/moz.build
@@ -152,3 +152,6 @@ if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
 
 # Add libFuzzer configuration directives
 include('/tools/fuzzing/libfuzzer-config.mozbuild')
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/ipc/contentproc/moz.build b/ipc/contentproc/moz.build
index 07cf0b97c676..10e80926af53 100644
--- a/ipc/contentproc/moz.build
+++ b/ipc/contentproc/moz.build
@@ -23,3 +23,6 @@ if CONFIG['MOZ_SANDBOX'] and CONFIG['OS_ARCH'] == 'WINNT':
         '/security/sandbox/chromium',
         '/security/sandbox/chromium-shim',
     ]
+
+if CONFIG['MOZ_PGO'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/ipc/mscom/moz.build b/ipc/mscom/moz.build
index 1158e8c53666..5f425ceb806b 100644
--- a/ipc/mscom/moz.build
+++ b/ipc/mscom/moz.build
@@ -86,3 +86,6 @@ FINAL_LIBRARY = 'xul'
 
 with Files("**"):
     BUG_COMPONENT = ("Core", "IPC: MSCOM")
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/ipc/mscom/oop/moz.build b/ipc/mscom/oop/moz.build
index 8be7842b6e07..b2968575e32f 100644
--- a/ipc/mscom/oop/moz.build
+++ b/ipc/mscom/oop/moz.build
@@ -37,3 +37,6 @@ FORCE_STATIC_LIB = True
 # This DLL may be loaded into other processes, so we need static libs for
 # Windows 7 and Windows 8.
 USE_STATIC_LIBS = True
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/js/xpconnect/shell/moz.build b/js/xpconnect/shell/moz.build
index c9f1137bdab5..16d68399e6ca 100644
--- a/js/xpconnect/shell/moz.build
+++ b/js/xpconnect/shell/moz.build
@@ -53,3 +53,6 @@ if CONFIG['OS_ARCH'] == 'WINNT':
 CFLAGS += CONFIG['TK_CFLAGS']
 CXXFLAGS += CONFIG['TK_CFLAGS']
 OS_LIBS += CONFIG['TK_LIBS']
+
+if CONFIG['MOZ_PGO'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/js/xpconnect/src/moz.build b/js/xpconnect/src/moz.build
index 7a03e1944400..f4b2bec0fea1 100644
--- a/js/xpconnect/src/moz.build
+++ b/js/xpconnect/src/moz.build
@@ -64,3 +64,6 @@ if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
 
 if CONFIG['NIGHTLY_BUILD']:
     DEFINES['ENABLE_WASM_GC'] = True
+
+if CONFIG['MOZ_ASAN'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/layout/painting/moz.build b/layout/painting/moz.build
index d3822336c572..c832f5c1a050 100644
--- a/layout/painting/moz.build
+++ b/layout/painting/moz.build
@@ -75,3 +75,6 @@ if CONFIG['CC_TYPE'] in ('msvc', 'clang-cl'):
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/media/gmp-clearkey/0.1/moz.build b/media/gmp-clearkey/0.1/moz.build
index 5ec857652384..9b18b4dd1c6f 100644
--- a/media/gmp-clearkey/0.1/moz.build
+++ b/media/gmp-clearkey/0.1/moz.build
@@ -78,3 +78,6 @@ elif CONFIG['CC_TYPE'] in ('msvc', 'clang-cl'):
     CFLAGS += [
         '-FI', 'stdio.h',           # for sprintf() prototype
     ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/media/mtransport/common.build b/media/mtransport/common.build
index fe7ea2c359c3..dfd8d165665b 100644
--- a/media/mtransport/common.build
+++ b/media/mtransport/common.build
@@ -93,3 +93,6 @@ DEFINES['R_DEFINED_UINT8'] = 'uint64_t'
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/media/mtransport/third_party/nICEr/nicer.gyp b/media/mtransport/third_party/nICEr/nicer.gyp
index 4827eb5b7485..cb383fe9a98f 100644
--- a/media/mtransport/third_party/nICEr/nicer.gyp
+++ b/media/mtransport/third_party/nICEr/nicer.gyp
@@ -207,6 +207,7 @@
               # Windows, clang-cl build
               [ 'clang_cl == 1', {
                 'cflags_mozilla': [
+                    '-Wno-error', # workaround for bug 1090497
                     '-Xclang',
                     '-Wall',
                     '-Wno-parentheses',
diff --git a/media/mtransport/third_party/nrappkit/nrappkit.gyp b/media/mtransport/third_party/nrappkit/nrappkit.gyp
index 4c45da8dd6b2..4a8472eff6d6 100644
--- a/media/mtransport/third_party/nrappkit/nrappkit.gyp
+++ b/media/mtransport/third_party/nrappkit/nrappkit.gyp
@@ -204,6 +204,7 @@
               # Windows, clang-cl build
               [ 'clang_cl == 1', {
                 'cflags_mozilla': [
+                    '-Wno-error', # workaround for bug 1090497
                     '-Xclang',
                     '-Wall',
                     '-Wno-parentheses',
diff --git a/media/webrtc/signaling/gtest/moz.build b/media/webrtc/signaling/gtest/moz.build
index 85316c6b6473..6a4bd44eea81 100644
--- a/media/webrtc/signaling/gtest/moz.build
+++ b/media/webrtc/signaling/gtest/moz.build
@@ -48,3 +48,6 @@ if CONFIG['CC_TYPE'] in ('msvc', 'clang-cl'):
 
     # Disable warning for decorated name length exceeded, name was truncated
     CXXFLAGS += ['-wd4503']
+
+if CONFIG['MOZ_ASAN'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1306642
diff --git a/media/webrtc/signaling/src/media-conduit/moz.build b/media/webrtc/signaling/src/media-conduit/moz.build
index ef663638b2d9..0ee45385f806 100644
--- a/media/webrtc/signaling/src/media-conduit/moz.build
+++ b/media/webrtc/signaling/src/media-conduit/moz.build
@@ -35,3 +35,6 @@ if CONFIG['OS_TARGET'] == 'Android':
     ]
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['MOZ_ASAN'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1306642
diff --git a/media/webrtc/signaling/src/mediapipeline/moz.build b/media/webrtc/signaling/src/mediapipeline/moz.build
index b4c41d70a796..2a3c0b21e6ad 100644
--- a/media/webrtc/signaling/src/mediapipeline/moz.build
+++ b/media/webrtc/signaling/src/mediapipeline/moz.build
@@ -29,3 +29,6 @@ UNIFIED_SOURCES += [
 DEFINES['TRACING'] = True
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['MOZ_ASAN'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1306642
diff --git a/media/webrtc/signaling/src/sdp/moz.build b/media/webrtc/signaling/src/sdp/moz.build
index 3c51a33d3f4f..0099d16f3f61 100644
--- a/media/webrtc/signaling/src/sdp/moz.build
+++ b/media/webrtc/signaling/src/sdp/moz.build
@@ -61,3 +61,6 @@ SOURCES += [
 ]
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['ENABLE_CLANG_PLUGIN'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/memory/build/moz.build b/memory/build/moz.build
index e2c715271001..84e3d6281607 100644
--- a/memory/build/moz.build
+++ b/memory/build/moz.build
@@ -53,3 +53,6 @@ if CONFIG['MOZ_REPLACE_MALLOC_STATIC']:
     DEFINES['MOZ_REPLACE_MALLOC_STATIC'] = True
 
 DisableStlWrapping()
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/memory/replace/dmd/moz.build b/memory/replace/dmd/moz.build
index c6603df92a06..507ed84cbc7a 100644
--- a/memory/replace/dmd/moz.build
+++ b/memory/replace/dmd/moz.build
@@ -36,3 +36,6 @@ if CONFIG['OS_ARCH'] == 'WINNT':
     ]
 
 TEST_DIRS += ['test']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/memory/replace/logalloc/moz.build b/memory/replace/logalloc/moz.build
index d6ec145559dc..70aa8cf8104c 100644
--- a/memory/replace/logalloc/moz.build
+++ b/memory/replace/logalloc/moz.build
@@ -28,3 +28,6 @@ if CONFIG['OS_TARGET'] == 'Android' and FORCE_SHARED_LIB:
 DIRS += [
     'replay',
 ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/memory/replace/moz.build b/memory/replace/moz.build
index 4858b3379015..49e6966eb537 100644
--- a/memory/replace/moz.build
+++ b/memory/replace/moz.build
@@ -18,3 +18,6 @@ DIRS += [
 
 if CONFIG['MOZ_DMD']:
     DIRS += ['dmd']
+
+if CONFIG['MOZ_DEBUG'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/mozglue/build/moz.build b/mozglue/build/moz.build
index b3d9dfc387fe..674ab453800c 100644
--- a/mozglue/build/moz.build
+++ b/mozglue/build/moz.build
@@ -134,3 +134,6 @@ if CONFIG['MOZ_LINKER'] and CONFIG['CPU_ARCH'] == 'arm':
     LDFLAGS += ['-Wl,-version-script,%s/arm-eabi-filter' % SRCDIR]
 
 DIST_INSTALL = True
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/mozglue/tests/gtest/InjectorDLL/moz.build b/mozglue/tests/gtest/InjectorDLL/moz.build
index 9f60e9443373..053221dd61b6 100644
--- a/mozglue/tests/gtest/InjectorDLL/moz.build
+++ b/mozglue/tests/gtest/InjectorDLL/moz.build
@@ -13,3 +13,6 @@ UNIFIED_SOURCES = [
 
 if CONFIG['COMPILE_ENVIRONMENT']:
     TEST_HARNESS_FILES.gtest += ['!InjectorDLL.dll']
+
+if CONFIG['MOZ_PGO'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/mozglue/tests/interceptor/moz.build b/mozglue/tests/interceptor/moz.build
index 9a69037d6d56..a0f205907263 100644
--- a/mozglue/tests/interceptor/moz.build
+++ b/mozglue/tests/interceptor/moz.build
@@ -21,3 +21,6 @@ if CONFIG['OS_TARGET'] == 'WINNT' and CONFIG['CC_TYPE'] == 'gcc':
     LDFLAGS += [
         '-municode',
     ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/netwerk/base/moz.build b/netwerk/base/moz.build
index 8919361fb07c..f15746302ea0 100644
--- a/netwerk/base/moz.build
+++ b/netwerk/base/moz.build
@@ -306,3 +306,6 @@ LOCAL_INCLUDES += [
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/netwerk/cookie/moz.build b/netwerk/cookie/moz.build
index 96a406b14a83..e84cb3cb6a10 100644
--- a/netwerk/cookie/moz.build
+++ b/netwerk/cookie/moz.build
@@ -55,3 +55,6 @@ FINAL_LIBRARY = 'xul'
 
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/netwerk/protocol/http/moz.build b/netwerk/protocol/http/moz.build
index cb1190cf9557..e02c78ff1f3a 100644
--- a/netwerk/protocol/http/moz.build
+++ b/netwerk/protocol/http/moz.build
@@ -143,3 +143,6 @@ if CONFIG['OS_TARGET'] == 'Darwin':
         DEFINES.update(
             HAS_CONNECTX=True,
         )
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/netwerk/wifi/moz.build b/netwerk/wifi/moz.build
index 7aef5e2e01f2..fcc85db476e9 100644
--- a/netwerk/wifi/moz.build
+++ b/netwerk/wifi/moz.build
@@ -54,3 +54,6 @@ if CONFIG['NECKO_WIFI_DBUS']:
     CXXFLAGS += CONFIG['MOZ_DBUS_GLIB_CFLAGS']
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/old-configure.in b/old-configure.in
index 169b90fa20b2..26e837297cfd 100644
--- a/old-configure.in
+++ b/old-configure.in
@@ -1044,12 +1044,7 @@ case "$target" in
         CXXFLAGS="$CXXFLAGS -D_SILENCE_TR1_NAMESPACE_DEPRECATION_WARNING"
         LIBS="$LIBS kernel32.lib user32.lib gdi32.lib winmm.lib wsock32.lib advapi32.lib secur32.lib"
         MOZ_DEBUG_LDFLAGS='-DEBUG -DEBUGTYPE:CV'
-        # -Werror is disabled on clang-cl until bug 1090497 cleans up the noise.
-        if test -n "$CLANG_CL"; then
-            WARNINGS_AS_ERRORS=''
-        else
-            WARNINGS_AS_ERRORS='-WX'
-        fi
+        WARNINGS_AS_ERRORS='-WX'
         # Use a higher optimization level for clang-cl, so we can come closer
         # to MSVC's performance numbers (see bug 1443590).
         if test -n "$CLANG_CL"; then
diff --git a/security/certverifier/moz.build b/security/certverifier/moz.build
index d694e3c4ead6..fcb639aa35fa 100644
--- a/security/certverifier/moz.build
+++ b/security/certverifier/moz.build
@@ -144,3 +144,6 @@ if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     ]
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/security/manager/ssl/moz.build b/security/manager/ssl/moz.build
index 3f08c8fd08c4..e642a504550d 100644
--- a/security/manager/ssl/moz.build
+++ b/security/manager/ssl/moz.build
@@ -219,3 +219,6 @@ if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += [
         '-Wno-unused-parameter',
     ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/security/pkix/test/gtest/moz.build b/security/pkix/test/gtest/moz.build
index d9fa10e60da2..23edde55bdc9 100644
--- a/security/pkix/test/gtest/moz.build
+++ b/security/pkix/test/gtest/moz.build
@@ -70,3 +70,6 @@ elif CONFIG['CC_TYPE'] == 'msvc':
     # declaration of '*' hides class member
     '-wd4458',
   ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/security/pkix/warnings.mozbuild b/security/pkix/warnings.mozbuild
index f89d7fb74bed..182aa6773b57 100644
--- a/security/pkix/warnings.mozbuild
+++ b/security/pkix/warnings.mozbuild
@@ -10,6 +10,8 @@ if CONFIG['CC_TYPE'] in ('clang', 'clang-cl'):
     '-Wno-reserved-id-macro', # NSPR and NSS use reserved IDs in their include guards.
     '-Wno-weak-vtables', # We rely on the linker to merge the duplicate vtables.
   ]
+  if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
 elif CONFIG['CC_TYPE'] == 'msvc':
   CXXFLAGS += [
     '-sdl', # Enable additional security checks based on Microsoft's SDL.
diff --git a/security/sandbox/moz.build b/security/sandbox/moz.build
index bdc5e8492a50..db0449b11add 100755
--- a/security/sandbox/moz.build
+++ b/security/sandbox/moz.build
@@ -178,3 +178,6 @@ elif CONFIG['OS_ARCH'] == 'WINNT':
             '-wd4311', # 'reinterpret_cast': pointer truncation from 'LPOVERLAPPED' to 'DWORD'
             '-wd4312', # 'reinterpret_cast': conversion from 'DWORD' to 'LPOVERLAPPED' of greater size
         ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/security/sandbox/win/src/sandboxbroker/moz.build b/security/sandbox/win/src/sandboxbroker/moz.build
index cf97b038865b..f06bd3c6955c 100644
--- a/security/sandbox/win/src/sandboxbroker/moz.build
+++ b/security/sandbox/win/src/sandboxbroker/moz.build
@@ -19,3 +19,6 @@ LOCAL_INCLUDES += ['/security/sandbox/chromium-shim']
 LOCAL_INCLUDES += ['/security/sandbox/chromium']
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/testing/tools/fileid/moz.build b/testing/tools/fileid/moz.build
index ce5e36888a52..75862b7d7bff 100644
--- a/testing/tools/fileid/moz.build
+++ b/testing/tools/fileid/moz.build
@@ -38,3 +38,5 @@ if CONFIG['OS_ARCH'] == 'Linux' or CONFIG['OS_ARCH'] == 'Darwin':
         '/toolkit/crashreporter/google-breakpad/src',
     ]
 
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/testing/tools/minidumpwriter/moz.build b/testing/tools/minidumpwriter/moz.build
index 945856ef6de2..f32ca28ae821 100644
--- a/testing/tools/minidumpwriter/moz.build
+++ b/testing/tools/minidumpwriter/moz.build
@@ -17,3 +17,6 @@ if CONFIG['ENABLE_TESTS'] and CONFIG['CPU_ARCH'] == 'x86_64' and CONFIG['OS_ARCH
         WIN32_EXE_LDFLAGS += ['-municode']
 
 NO_PGO = True
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/components/build/moz.build b/toolkit/components/build/moz.build
index 67c5c73349dd..76a609253eb6 100644
--- a/toolkit/components/build/moz.build
+++ b/toolkit/components/build/moz.build
@@ -37,3 +37,6 @@ if not CONFIG['MOZ_DISABLE_PARENTAL_CONTROLS']:
     LOCAL_INCLUDES += [
         '../parentalcontrols',
     ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/components/extensions/moz.build b/toolkit/components/extensions/moz.build
index ccdfb4c206b7..d0418916a40d 100644
--- a/toolkit/components/extensions/moz.build
+++ b/toolkit/components/extensions/moz.build
@@ -98,3 +98,6 @@ with Files('docs/**'):
     SCHEDULES.exclusive = ['docs']
 
 include('/ipc/chromium/chromium-config.mozbuild')
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/components/jsoncpp/src/lib_json/moz.build b/toolkit/components/jsoncpp/src/lib_json/moz.build
index 6920229e1ea1..e515c5680673 100644
--- a/toolkit/components/jsoncpp/src/lib_json/moz.build
+++ b/toolkit/components/jsoncpp/src/lib_json/moz.build
@@ -51,3 +51,6 @@ if CONFIG['CC_TYPE'] in ('clang', 'clang-cl', 'gcc'):
     CXXFLAGS += [
         '-Wno-implicit-fallthrough',
     ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/components/maintenanceservice/moz.build b/toolkit/components/maintenanceservice/moz.build
index ff6c6ad8d980..5b5b5f61b332 100644
--- a/toolkit/components/maintenanceservice/moz.build
+++ b/toolkit/components/maintenanceservice/moz.build
@@ -47,3 +47,6 @@ OS_LIBS += [
 
 with Files('**'):
     BUG_COMPONENT = ('Toolkit', 'Application Update')
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/components/osfile/moz.build b/toolkit/components/osfile/moz.build
index a3367f0b61b4..47d5f7e11567 100644
--- a/toolkit/components/osfile/moz.build
+++ b/toolkit/components/osfile/moz.build
@@ -33,3 +33,7 @@ FINAL_LIBRARY = 'xul'
 
 with Files('**'):
     BUG_COMPONENT = ('Toolkit', 'OS.File')
+
+if (not CONFIG['HAVE_64BIT_BUILD'] and
+    CONFIG['ENABLE_CLANG_PLUGIN'] and CONFIG['CC_TYPE'] == 'clang-cl'):
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/components/reputationservice/moz.build b/toolkit/components/reputationservice/moz.build
index dd90dafb4883..b8917ca19c82 100644
--- a/toolkit/components/reputationservice/moz.build
+++ b/toolkit/components/reputationservice/moz.build
@@ -42,3 +42,6 @@ if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-shadow']
 
 include('/ipc/chromium/chromium-config.mozbuild')
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/components/telemetry/pingsender/moz.build b/toolkit/components/telemetry/pingsender/moz.build
index c4187d9e4831..32becbeed777 100644
--- a/toolkit/components/telemetry/pingsender/moz.build
+++ b/toolkit/components/telemetry/pingsender/moz.build
@@ -36,3 +36,6 @@ else:
 # Don't use the STL wrappers; we don't link with -lmozalloc, and it really
 # doesn't matter here anyway.
 DisableStlWrapping()
+
+if CONFIG['MOZ_DEBUG'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/components/url-classifier/moz.build b/toolkit/components/url-classifier/moz.build
index 67bc4dc22792..ecb61bbbb395 100644
--- a/toolkit/components/url-classifier/moz.build
+++ b/toolkit/components/url-classifier/moz.build
@@ -98,3 +98,6 @@ with Files('docs/**'):
     SCHEDULES.exclusive = ['docs']
 
 include('/ipc/chromium/chromium-config.mozbuild')
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/components/url-classifier/tests/gtest/moz.build b/toolkit/components/url-classifier/tests/gtest/moz.build
index 28a21b85e877..3aae469e082b 100644
--- a/toolkit/components/url-classifier/tests/gtest/moz.build
+++ b/toolkit/components/url-classifier/tests/gtest/moz.build
@@ -36,3 +36,6 @@ if CONFIG['NIGHTLY_BUILD'] or CONFIG['MOZ_DEBUG']:
     DEFINES['MOZ_SAFEBROWSING_DUMP_FAILED_UPDATES'] = True
 
 FINAL_LIBRARY = 'xul-gtest'
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/crashreporter/client/moz.build b/toolkit/crashreporter/client/moz.build
index 55f89ef4ff23..277502fac9f5 100644
--- a/toolkit/crashreporter/client/moz.build
+++ b/toolkit/crashreporter/client/moz.build
@@ -98,3 +98,6 @@ RCINCLUDE = 'crashreporter.rc'
 DisableStlWrapping()
 
 include('/toolkit/crashreporter/crashreporter.mozbuild')
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/crashreporter/google-breakpad/src/processor/moz.build b/toolkit/crashreporter/google-breakpad/src/processor/moz.build
index 9cc00f162d34..9e992f0b246e 100644
--- a/toolkit/crashreporter/google-breakpad/src/processor/moz.build
+++ b/toolkit/crashreporter/google-breakpad/src/processor/moz.build
@@ -61,3 +61,6 @@ Library('breakpad_processor')
 DisableStlWrapping()
 
 include('/toolkit/crashreporter/crashreporter.mozbuild')
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/crashreporter/minidump-analyzer/moz.build b/toolkit/crashreporter/minidump-analyzer/moz.build
index 70f3b259a9d8..3df941ee8493 100644
--- a/toolkit/crashreporter/minidump-analyzer/moz.build
+++ b/toolkit/crashreporter/minidump-analyzer/moz.build
@@ -59,3 +59,6 @@ if CONFIG['OS_TARGET'] != 'WINNT':
     DisableStlWrapping()
 
 include('/toolkit/crashreporter/crashreporter.mozbuild')
+
+if CONFIG['MOZ_PGO'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/crashreporter/moz.build b/toolkit/crashreporter/moz.build
index f726be233cc9..c5e8b111d323 100644
--- a/toolkit/crashreporter/moz.build
+++ b/toolkit/crashreporter/moz.build
@@ -128,3 +128,6 @@ else:
 
 with Files('**'):
     BUG_COMPONENT = ('Toolkit', 'Crash Reporting')
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/crashreporter/test/moz.build b/toolkit/crashreporter/test/moz.build
index bb66db995a20..23a19d5dd4ca 100755
--- a/toolkit/crashreporter/test/moz.build
+++ b/toolkit/crashreporter/test/moz.build
@@ -58,3 +58,6 @@ NO_PGO = True
 # Temporary workaround for an issue in upstream breakpad
 if CONFIG['CC_TYPE'] in ('msvc', 'clang-cl'):
     CXXFLAGS += ['-wd4334']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
\ No newline at end of file
diff --git a/toolkit/mozapps/update/common/moz.build b/toolkit/mozapps/update/common/moz.build
index 9b382019cab4..197f19d43b9e 100644
--- a/toolkit/mozapps/update/common/moz.build
+++ b/toolkit/mozapps/update/common/moz.build
@@ -50,3 +50,6 @@ SOURCES += [
     'readstrings.cpp',
     'updatecommon.cpp',
 ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/mozapps/update/updater/updater-common.build b/toolkit/mozapps/update/updater/updater-common.build
index c446f2b35a60..0d4f18d37838 100644
--- a/toolkit/mozapps/update/updater/updater-common.build
+++ b/toolkit/mozapps/update/updater/updater-common.build
@@ -114,3 +114,5 @@ if 'gtk' in CONFIG['MOZ_WIDGET_TOOLKIT']:
 if CONFIG['CC_TYPE'] == 'gcc':
     CXXFLAGS += ['-Wno-format-truncation']
 
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/system/windowsDHCPClient/moz.build b/toolkit/system/windowsDHCPClient/moz.build
index 3124e393a89d..ab0d26565955 100644
--- a/toolkit/system/windowsDHCPClient/moz.build
+++ b/toolkit/system/windowsDHCPClient/moz.build
@@ -15,4 +15,7 @@ SOURCES += [
     'WindowsNetworkFunctionsWrapper.cpp'
 ]
 
-FINAL_LIBRARY = 'xul'
\ No newline at end of file
+FINAL_LIBRARY = 'xul'
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/system/windowsDHCPClient/tests/gtest/moz.build b/toolkit/system/windowsDHCPClient/tests/gtest/moz.build
index cb0e5f8ddd08..7ff910c8decb 100644
--- a/toolkit/system/windowsDHCPClient/tests/gtest/moz.build
+++ b/toolkit/system/windowsDHCPClient/tests/gtest/moz.build
@@ -18,4 +18,7 @@ LOCAL_INCLUDES += [
 FINAL_LIBRARY = 'xul-gtest'
 
 if CONFIG['GNU_CXX']:
-    CXXFLAGS += ['-Wshadow']
\ No newline at end of file
+    CXXFLAGS += ['-Wshadow']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/xre/moz.build b/toolkit/xre/moz.build
index 65778b8841e3..dda6846d0489 100644
--- a/toolkit/xre/moz.build
+++ b/toolkit/xre/moz.build
@@ -234,3 +234,6 @@ if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
 
 if CONFIG['MOZ_IPDL_TESTS']:
     DEFINES['MOZ_IPDL_TESTS'] = True
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/toolkit/xre/test/win/moz.build b/toolkit/xre/test/win/moz.build
index 9a46eb3b1147..c18abfd81aeb 100644
--- a/toolkit/xre/test/win/moz.build
+++ b/toolkit/xre/test/win/moz.build
@@ -23,3 +23,6 @@ OS_LIBS += [
     'shell32',
     'ws2_32',
 ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/tools/profiler/moz.build b/tools/profiler/moz.build
index 53b69801a170..0752d81b4e6e 100644
--- a/tools/profiler/moz.build
+++ b/tools/profiler/moz.build
@@ -153,3 +153,6 @@ if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
 
 with Files('**'):
     BUG_COMPONENT = ('Core', 'Gecko Profiler')
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/widget/windows/moz.build b/widget/windows/moz.build
index 762323302494..2089a6f256c4 100644
--- a/widget/windows/moz.build
+++ b/widget/windows/moz.build
@@ -166,3 +166,6 @@ OS_LIBS += [
 if CONFIG['CC_TYPE'] in ('msvc', 'clang-cl'):
     # C5038: Suppress initializer list order warnings from wrl.h
     SOURCES['WindowsUIUtils.cpp'].flags += ['-wd5038']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/xpcom/base/moz.build b/xpcom/base/moz.build
index f761ccee1cc5..c2dbba28fddc 100644
--- a/xpcom/base/moz.build
+++ b/xpcom/base/moz.build
@@ -217,3 +217,6 @@ LOCAL_INCLUDES += [
 
 if 'gtk' in CONFIG['MOZ_WIDGET_TOOLKIT']:
     CXXFLAGS += CONFIG['TK_CFLAGS']
+
+if CONFIG['ENABLE_CLANG_PLUGIN'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/xpcom/glue/objs.mozbuild b/xpcom/glue/objs.mozbuild
index 3c4ea23614df..b55690438f9c 100644
--- a/xpcom/glue/objs.mozbuild
+++ b/xpcom/glue/objs.mozbuild
@@ -19,3 +19,6 @@ xpcom_gluens_src_lcppsrcs = [
 xpcom_gluens_src_cppsrcs = [
     '/xpcom/glue/%s' % s for s in xpcom_gluens_src_lcppsrcs
 ]
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/xpcom/io/moz.build b/xpcom/io/moz.build
index 5947a04eb494..4dd0def517e3 100644
--- a/xpcom/io/moz.build
+++ b/xpcom/io/moz.build
@@ -157,3 +157,6 @@ if CONFIG['CC_TYPE'] in ('msvc', 'clang-cl'):
     # '_snwprintf' : format string '%s' requires an argument of type 'wchar_t *',
     # but variadic argument 3 has type 'char16ptr_t'
     CXXFLAGS += ['-wd4477']
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/xpcom/threads/moz.build b/xpcom/threads/moz.build
index 6743ce779c23..e57bf639458f 100644
--- a/xpcom/threads/moz.build
+++ b/xpcom/threads/moz.build
@@ -119,3 +119,6 @@ LOCAL_INCLUDES += [
 FINAL_LIBRARY = 'xul'
 
 include('/ipc/chromium/chromium-config.mozbuild')
+
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497
diff --git a/xpcom/windbgdlg/moz.build b/xpcom/windbgdlg/moz.build
index f0343d31ae6f..a8442bc1fa28 100644
--- a/xpcom/windbgdlg/moz.build
+++ b/xpcom/windbgdlg/moz.build
@@ -7,3 +7,6 @@
 SimplePrograms([
     'windbgdlg'
 ])
+
+if CONFIG['MOZ_DEBUG'] and CONFIG['CC_TYPE'] == 'clang-cl':
+    AllowCompilerWarnings()  # workaround for bug 1090497