diff --git a/config/config.mk b/config/config.mk
index 03c402590dee..8755899234d7 100644
--- a/config/config.mk
+++ b/config/config.mk
@@ -312,8 +312,8 @@ CXXFLAGS += $(WARNINGS_AS_ERRORS)
 CFLAGS   += $(WARNINGS_AS_ERRORS)
 endif # ALLOW_COMPILER_WARNINGS
 
-COMPILE_CFLAGS	= $(COMPUTED_CFLAGS) $(RTL_FLAGS) $(OS_COMPILE_CFLAGS) $(_DEPEND_CFLAGS) $(CFLAGS) $(MOZBUILD_CFLAGS) $(MK_COMPILE_DEFINES)
-COMPILE_CXXFLAGS = $(COMPUTED_CXXFLAGS) $(RTL_FLAGS) $(OS_COMPILE_CXXFLAGS) $(_DEPEND_CFLAGS) $(CXXFLAGS) $(MOZBUILD_CXXFLAGS) $(MK_COMPILE_DEFINES)
+COMPILE_CFLAGS	= $(COMPUTED_CFLAGS) $(OS_COMPILE_CFLAGS) $(_DEPEND_CFLAGS) $(CFLAGS) $(MOZBUILD_CFLAGS) $(MK_COMPILE_DEFINES)
+COMPILE_CXXFLAGS = $(COMPUTED_CXXFLAGS) $(OS_COMPILE_CXXFLAGS) $(_DEPEND_CFLAGS) $(CXXFLAGS) $(MOZBUILD_CXXFLAGS) $(MK_COMPILE_DEFINES)
 COMPILE_CMFLAGS = $(OS_COMPILE_CMFLAGS) $(MOZBUILD_CMFLAGS)
 COMPILE_CMMFLAGS = $(OS_COMPILE_CMMFLAGS) $(MOZBUILD_CMMFLAGS)
 ASFLAGS += $(MOZBUILD_ASFLAGS)
diff --git a/python/mozbuild/mozbuild/compilation/database.py b/python/mozbuild/mozbuild/compilation/database.py
index 0ac060ccd3e0..a051a5adfe4d 100644
--- a/python/mozbuild/mozbuild/compilation/database.py
+++ b/python/mozbuild/mozbuild/compilation/database.py
@@ -76,8 +76,7 @@ class CompileDBBackend(CommonBackend):
 
         elif isinstance(obj, VariablePassthru):
             for var in ('MOZBUILD_CFLAGS', 'MOZBUILD_CXXFLAGS',
-                        'MOZBUILD_CMFLAGS', 'MOZBUILD_CMMFLAGS',
-                        'RTL_FLAGS'):
+                        'MOZBUILD_CMFLAGS', 'MOZBUILD_CMMFLAGS'):
                 if var in obj.variables:
                     self._local_flags[obj.objdir][var] = obj.variables[var]
             if (obj.variables.get('ALLOW_COMPILER_WARNINGS') and
@@ -196,8 +195,6 @@ class CompileDBBackend(CommonBackend):
 
         db.append('$(COMPUTED_%s)' % self.CFLAGS[canonical_suffix])
 
-        if canonical_suffix in ('.c', '.cpp'):
-            db.append('$(RTL_FLAGS)')
         append_var('OS_COMPILE_%s' % self.CFLAGS[canonical_suffix])
         append_var('OS_CPPFLAGS')
         append_var('OS_%s' % self.CFLAGS[canonical_suffix])
diff --git a/python/mozbuild/mozbuild/frontend/context.py b/python/mozbuild/mozbuild/frontend/context.py
index e286365d59d0..5f842c409091 100644
--- a/python/mozbuild/mozbuild/frontend/context.py
+++ b/python/mozbuild/mozbuild/frontend/context.py
@@ -323,6 +323,7 @@ class CompileFlags(ContextDerivedValue, dict):
              ('CXXFLAGS', 'CFLAGS')),
             ('DSO_PIC', context.config.substs.get('DSO_PIC_CFLAGS'),
              ('CXXFLAGS', 'CFLAGS')),
+            ('RTL', None, ('CXXFLAGS', 'CFLAGS')),
         )
         self._known_keys = set(k for k, v, _ in self.flag_variables)
 
diff --git a/python/mozbuild/mozbuild/frontend/emitter.py b/python/mozbuild/mozbuild/frontend/emitter.py
index aa3fd0cb3fcc..8952fa4fa15a 100644
--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -958,6 +958,8 @@ class TreeMetadataEmitter(LoggingMixin):
         elif dist_install is False:
             passthru.variables['NO_DIST_INSTALL'] = True
 
+        computed_flags = ComputedFlags(context, context['COMPILE_FLAGS'])
+
         # Ideally, this should be done in templates, but this is difficult at
         # the moment because USE_STATIC_LIBS can be set after a template
         # returns. Eventually, with context-based templates, it will be
@@ -972,6 +974,7 @@ class TreeMetadataEmitter(LoggingMixin):
                 rtl_flag += 'd'
             # Use a list, like MOZBUILD_*FLAGS variables
             passthru.variables['RTL_FLAGS'] = [rtl_flag]
+            computed_flags.resolve_flags('RTL', [rtl_flag])
 
         generated_files = set()
         for obj in self._process_generated_files(context):
@@ -985,8 +988,6 @@ class TreeMetadataEmitter(LoggingMixin):
             generated_files.add(str(sub.relpath))
             yield sub
 
-        computed_flags = ComputedFlags(context, context['COMPILE_FLAGS'])
-
         for defines_var, cls in (('DEFINES', Defines),
                                  ('HOST_DEFINES', HostDefines)):
             defines = context.get(defines_var)