diff --git a/doorcontrol-main.cgi b/doorcontrol-main.cgi
index 38a33cb..d5bc70c 100755
--- a/doorcontrol-main.cgi
+++ b/doorcontrol-main.cgi
@@ -13,6 +13,7 @@ LOCKFILE="./doorcontrol-main.lock"
 
 # Exit if instance already running
 if [ -e "$LOCKFILE" ]; then
+  echo '{"error": "running"}'
   exit 1
 else
   touch "$LOCKFILE"