diff --git a/DuetPkg/PostBuild.sh b/DuetPkg/PostBuild.sh
index aca66ad51b..4912fcf582 100644
--- a/DuetPkg/PostBuild.sh
+++ b/DuetPkg/PostBuild.sh
@@ -29,6 +29,7 @@ case "$1" in
      ;;
    *)
      echo Invalid Architecture string, should be only IA32 or X64
+     return 1
 esac
 
 #
@@ -78,3 +79,4 @@ then
 	echo Done!
 fi
 
+