diff --git a/Makefile.am b/Makefile.am
index 7380656..0df77f5 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -6,4 +6,4 @@ format:
 	clang-format -i -style=file $(FORMATSOURCES)
 
 check-format:
-	clang-format -i -style=file $(FORMATSOURCES) && git diff-index --quiet HEAD
+	clang-format -i -style=file $(FORMATSOURCES) && git diff --exit-code