diff --git a/clang/include/clang/Basic/Builtins.h b/clang/include/clang/Basic/Builtins.h
index 6d29b4315e5a7..d1c1ab44417fa 100644
--- a/clang/include/clang/Basic/Builtins.h
+++ b/clang/include/clang/Basic/Builtins.h
@@ -408,7 +408,8 @@ class Context {
 
   unsigned getRequiredVectorWidth(unsigned ID) const;
 
-  /// Return true if builtin ID belongs to AuxTarget.
+  /// Return true if the builtin ID belongs exclusively to the AuxTarget,
+  /// and false if it belongs to both primary and aux target, or neither.
   bool isAuxBuiltinID(unsigned ID) const {
     return ID >= (Builtin::FirstTSBuiltin + NumTargetBuiltins);
   }