diff --git a/scripts/99_deploy.sh b/scripts/99_deploy.sh
index bc00c95..e3b6471 100644
--- a/scripts/99_deploy.sh
+++ b/scripts/99_deploy.sh
@@ -81,7 +81,7 @@ firefox_profile_dir() {
 
     ffdir=/home/${user}/.mozilla/firefox/
 
-    if not [ -d "$ffdir" ]
+    if ! [ -d "$ffdir" ]
     then
         echo "firefox main directory not found: '${ffdir}'"
     else