Index: lib/Driver/ToolChains.cpp
===================================================================
--- lib/Driver/ToolChains.cpp
+++ lib/Driver/ToolChains.cpp
@@ -1225,13 +1225,18 @@
 }
 
 SanitizerMask Darwin::getSupportedSanitizers() const {
+  const bool IsX86_64 = getTriple().getArch() == llvm::Triple::x86_64;
   SanitizerMask Res = ToolChain::getSupportedSanitizers();
   Res |= SanitizerKind::Address;
   if (isTargetMacOS()) {
     if (!isMacosxVersionLT(10, 9))
       Res |= SanitizerKind::Vptr;
     Res |= SanitizerKind::SafeStack;
-    Res |= SanitizerKind::Thread;
+    if (IsX86_64)
+      Res |= SanitizerKind::Thread;
+  } else if (isTargetIOSSimulator() || isTargetTvOSSimulator()) {
+    if (IsX86_64)
+      Res |= SanitizerKind::Thread;
   }
   return Res;
 }
Index: test/Driver/fsanitize.c
===================================================================
--- test/Driver/fsanitize.c
+++ test/Driver/fsanitize.c
@@ -217,6 +217,15 @@
 // CHECK-TSAN-MSAN-MSAN-DARWIN: unsupported option '-fsanitize=memory' for target 'x86_64-apple-darwin10'
 // CHECK-TSAN-MSAN-MSAN-DARWIN-NOT: unsupported option
 
+// RUN: %clang -target x86_64-apple-darwin10 -fsanitize=thread %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-TSAN-X86-64-DARWIN
+// CHECK-TSAN-X86-64-DARWIN-NOT: unsupported option
+
+// RUN: %clang -target i386-apple-darwin10 -fsanitize=thread %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-TSAN-I386-DARWIN
+// CHECK-TSAN-I386-DARWIN: unsupported option '-fsanitize=thread' for target 'i386-apple-darwin10'
+
+// RUN: %clang -target arm-apple-darwin10 -fsanitize=thread %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-TSAN-ARM-DARWIN
+// CHECK-TSAN-ARM-DARWIN: unsupported option '-fsanitize=thread' for target 'arm-apple-darwin10'
+
 // RUN: %clang -target x86_64-apple-darwin10 -fsanitize=function %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FSAN-DARWIN
 // CHECK-FSAN-DARWIN: unsupported option '-fsanitize=function' for target 'x86_64-apple-darwin10'