diff --git a/projectionscreen.sh b/projectionscreen.sh
index 9f7c3bc..acd9b56 100755
--- a/projectionscreen.sh
+++ b/projectionscreen.sh
@@ -28,4 +28,5 @@ case "$1" in
       ;;
   stop) rollstop
       ;;
+  *) echo "usage: $0 {up|down|stop}"
 esac