diff --git a/Makefile b/Makefile
index 2ba06cf..f2ff064 100644
--- a/Makefile
+++ b/Makefile
@@ -8,9 +8,9 @@ TARGET_DIRS:=./whispering
 flake8:
 	find $(TARGET_DIRS) | grep '\.py$$' | xargs flake8
 black:
-	find $(TARGET_DIRS) | grep '\.py$$' | xargs black --diff | diff /dev/null -
+	find $(TARGET_DIRS) | grep '\.py$$' | xargs black --diff | python ./scripts/check_null.py
 isort:
-	find $(TARGET_DIRS) | grep '\.py$$' | xargs isort --diff | diff /dev/null -
+	find $(TARGET_DIRS) | grep '\.py$$' | xargs isort --diff | python ./scripts/check_null.py
 pydocstyle:
 	find $(TARGET_DIRS) | grep -v tests | xargs pydocstyle --ignore=D100,D101,D102,D103,D104,D105,D107,D203,D212
 pytest:
diff --git a/scripts/check_null.py b/scripts/check_null.py
new file mode 100644
index 0000000..b797863
--- /dev/null
+++ b/scripts/check_null.py
@@ -0,0 +1,13 @@
+#!/usr/bin/env python3
+
+import sys
+
+
+def main() -> None:
+    data = sys.stdin.read()
+    if len(data) != 0:
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()