diff --git a/coco/gen-grammar b/coco/gen-grammar
index 1c4b079..222883c 100755
--- a/coco/gen-grammar
+++ b/coco/gen-grammar
@@ -1,5 +1,5 @@
-COCO_EXECUTABLE= $1 || "cococpp"
+COCO_EXECUTABLE=${1:-cococpp}
 
 echo "Run coco generator: "
 $COCO_EXECUTABLE ./xreate.ATG 
     #-frames $COCO_PATH