diff --git a/Makefile b/Makefile
index b4703e48fec93075cd5e3ddd83469705d2fee8f8..1e1866be3da1ba4520911eb27016544de419161b 100644
--- a/Makefile
+++ b/Makefile
@@ -148,6 +148,7 @@ while test $$# -gt 0 ; do
       ;;
     --*)
       usage
+      exit 1
       ;;
     *)
       break