diff --git a/mail/app/no-pie/moz.build b/mail/app/no-pie/moz.build
index 5fb032bd33..74aa89409d 100644
--- a/mail/app/no-pie/moz.build
+++ b/mail/app/no-pie/moz.build
@@ -17,6 +17,8 @@ CFLAGS += [
 
 # Use OS_LIBS instead of LDFLAGS to "force" the flag to come after -pie
 # from MOZ_PROGRAM_LDFLAGS.
-OS_LIBS += [
-    "-no-pie",
-]
+if CONFIG["CC_TYPE"] == "clang":
+    # clang < 5.0 doesn't support -no-pie.
+    OS_LIBS += ["-nopie"]
+else:
+    OS_LIBS += ["-no-pie"]
diff --git a/taskcluster/kinds/toolchain/clang.yml b/taskcluster/kinds/toolchain/clang.yml
index f9458a099d..7a8de97d91 100644
--- a/taskcluster/kinds/toolchain/clang.yml
+++ b/taskcluster/kinds/toolchain/clang.yml
@@ -21,12 +21,12 @@ job-defaults:
 # mozilla-central for Firefox builds, except that the Android compiler-rt
 # pieces have been left out.
 
-linux64-clang-18:
-    description: "Clang 18 toolchain build"
+linux64-clang-17:
+    description: "Clang 17 toolchain build"
     attributes:
         local-toolchain: true
     treeherder:
-        symbol: TL(clang-18)
+        symbol: TL(clang-17)
     worker-type: b-linux-gcp
     worker:
         max-run-time: 600
@@ -40,22 +40,22 @@ linux64-clang-18:
     fetches:
         toolchain:
             - linux64-cctools-port
-            - linux64-clang-18-raw
-            - linux64-aarch64-compiler-rt-18
-            - linux64-x64-compiler-rt-18
-            - linux64-x86-compiler-rt-18
-            - macosx64-aarch64-compiler-rt-18
-            - macosx64-x64-compiler-rt-18
-            - wasm32-wasi-compiler-rt-18
-            - win32-compiler-rt-18
-            - win64-compiler-rt-18
+            - linux64-clang-17-raw
+            - linux64-aarch64-compiler-rt-17
+            - linux64-x64-compiler-rt-17
+            - linux64-x86-compiler-rt-17
+            - macosx64-aarch64-compiler-rt-17
+            - macosx64-x64-compiler-rt-17
+            - wasm32-wasi-compiler-rt-17
+            - win32-compiler-rt-17
+            - win64-compiler-rt-17
 
-win64-clang-18:
-    description: "Clang-cl 18 toolchain build"
+win64-clang-17:
+    description: "Clang-cl 17 toolchain build"
     attributes:
         local-toolchain: true
     treeherder:
-        symbol: TW64(clang-18)
+        symbol: TW64(clang-17)
     worker-type: b-linux-gcp
     worker:
         max-run-time: 600
@@ -69,12 +69,12 @@ win64-clang-18:
     fetches:
         toolchain:
             - linux64-cctools-port
-            - win64-clang-18-raw
-            - linux64-aarch64-compiler-rt-18
-            - linux64-x64-compiler-rt-18
-            - linux64-x86-compiler-rt-18
-            - macosx64-aarch64-compiler-rt-18
-            - macosx64-x64-compiler-rt-18
-            - wasm32-wasi-compiler-rt-18
-            - win32-compiler-rt-18
-            - win64-compiler-rt-18
+            - win64-clang-17-raw
+            - linux64-aarch64-compiler-rt-17
+            - linux64-x64-compiler-rt-17
+            - linux64-x86-compiler-rt-17
+            - macosx64-aarch64-compiler-rt-17
+            - macosx64-x64-compiler-rt-17
+            - wasm32-wasi-compiler-rt-17
+            - win32-compiler-rt-17
+            - win64-compiler-rt-17
diff --git a/taskcluster/kinds/toolchain/kind.yml b/taskcluster/kinds/toolchain/kind.yml
index fb01696c78..3354dd7a06 100644
--- a/taskcluster/kinds/toolchain/kind.yml
+++ b/taskcluster/kinds/toolchain/kind.yml
@@ -10,12 +10,12 @@ kind-dependencies:
     - packages
 
 reference-jobs:
-    - linux64-aarch64-compiler-rt-18
+    - linux64-aarch64-compiler-rt-17
     - linux64-cargo-vet
     - linux64-cbindgen
     - linux64-cctools-port
-    - linux64-clang-18-profile
-    - linux64-clang-18-raw
+    - linux64-clang-17-profile
+    - linux64-clang-17-raw
     - linux64-clang-mingw-x64
     - linux64-clang-mingw-x86
     - linux64-clang-tidy
@@ -50,18 +50,18 @@ reference-jobs:
     - linux64-upx
     - linux64-winchecksec
     - linux64-wine
-    - linux64-x64-compiler-rt-18
-    - linux64-x86-compiler-rt-18
+    - linux64-x64-compiler-rt-17
+    - linux64-x86-compiler-rt-17
     - linux64-xar
-    - macosx64-aarch64-compiler-rt-18
-    - macosx64-clang-18-raw
+    - macosx64-aarch64-compiler-rt-17
+    - macosx64-clang-17-raw
     - macosx64-fix-stacks
     - macosx64-grcov
     - macosx64-minidump-stackwalk
     - macosx64-node
     - macosx64-sdk
     - macosx64-sdk-toolchain
-    - macosx64-x64-compiler-rt-18
+    - macosx64-x64-compiler-rt-17
     - mingw32-rust
     - nsis
     - sysroot-aarch64-linux-gnu
@@ -69,15 +69,15 @@ reference-jobs:
     - sysroot-wasm32-wasi
     - sysroot-x86_64-linux-gnu
     - vs
-    - wasm32-wasi-compiler-rt-18
-    - win32-compiler-rt-18
+    - wasm32-wasi-compiler-rt-17
+    - win32-compiler-rt-17
     - win32-fix-stacks
     - win32-minidump-stackwalk
     - win32-node
     - win64-cbindgen
-    - win64-clang-18-raw
-    - win64-clang-18-stage1
-    - win64-compiler-rt-18
+    - win64-clang-17-raw
+    - win64-clang-17-stage1
+    - win64-compiler-rt-17
     - win64-libxml2
     - win64-dump_syms
     - win64-grcov