diff --git a/clang-tools-extra/test/clang-tidy/check_clang_tidy.py b/clang-tools-extra/test/clang-tidy/check_clang_tidy.py
index d80a28044ea0a..3eaba0e9dff3a 100755
--- a/clang-tools-extra/test/clang-tidy/check_clang_tidy.py
+++ b/clang-tools-extra/test/clang-tidy/check_clang_tidy.py
@@ -391,9 +391,7 @@ def parse_arguments() -> Tuple[argparse.Namespace, List[str]]:
     args, extra_args = parser.parse_known_args()
     if args.std is None:
         _, extension = os.path.splitext(args.assume_filename or args.input_file_name)
-        args.std = [
-            "c++11-or-later" if extension in [".cpp", ".hpp", ".mm"] else "c99-or-later"
-        ]
+        args.std = ["c99-or-later" if extension in [".c", ".m"] else "c++11-or-later"]
 
     return (args, extra_args)