diff --git a/lib/parse_udp.js b/lib/parse_udp.js
index 2c1ee8e..7e5ccdf 100644
--- a/lib/parse_udp.js
+++ b/lib/parse_udp.js
@@ -57,7 +57,7 @@ function parseUdpRequest (msg, rinfo) {
       throw new Error('multiple info_hash scrape not supported')
     }
   } else {
-    return null
+    throw new Error('Invalid action in UDP packet: ' + params.action)
   }
 
   return params