diff --git a/test/Makefile b/test/Makefile
index b416bc3..08c6eab 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -351,7 +351,7 @@
 .PHONY: checkstyle-python-all
 checkstyle-python-all: $(PIP_INSTALL_DONE)
 	@bash -c "source $(VENV_PATH)/bin/activate &&\
-		black -t py39 --diff $(WS_ROOT) ||\
+		black -t py39 --check --diff $(WS_ROOT) ||\
 		(echo \"*************************************************************************\" &&\
 		echo \"* Test framework PEP8 compliance check FAILED (maybe: make fixstyle-python)\" &&\
 		echo \"*************************************************************************\" &&\