diff --git a/gridworks b/gridworks
index 6ab72a125..8106e8c69 100755
--- a/gridworks
+++ b/gridworks
@@ -87,7 +87,7 @@ load_configs() {
 }
     
 check_macosx() {
-    if [ -z "$DARWIN" ] ; then
+    if ! $DARWIN ; then
         error "This action can only run on MacOSX"
     fi
 }