diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 403a5c9ed0fe..1741755723ad 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -811,7 +811,7 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
     // FIXME: This is target-dependent.
     Builder.defineMacro("__GCC_ATOMIC_TEST_AND_SET_TRUEVAL", "1");
 
-    // Used by libstdc++ to implement ATOMIC_<foo>_LOCK_FREE.
+    // Used by libc++ and libstdc++ to implement ATOMIC_<foo>_LOCK_FREE.
     unsigned InlineWidthBits = TI.getMaxAtomicInlineWidth();
 #define DEFINE_LOCK_FREE_MACRO(TYPE, Type) \
     Builder.defineMacro("__GCC_ATOMIC_" #TYPE "_LOCK_FREE", \