diff --git a/scripts/xflock4 b/scripts/xflock4
index 7d857d3..5b1313c 100644
--- a/scripts/xflock4
+++ b/scripts/xflock4
@@ -33,7 +33,9 @@ for lock_cmd in \
     "xscreensaver-command -lock" \
     "gnome-screensaver-command --lock"
 do
-    $lock_cmd >/dev/null 2>&1 && exit
+  if [ ! -z "$lock_cmd" ]; then
+      $lock_cmd >/dev/null 2>&1 && exit
+  fi
 done
 
 # else run another access locking utility, if installed