diff --git a/modules/phenyl-http-rules/src/decode-request.js b/modules/phenyl-http-rules/src/decode-request.js
index <HASH>..<HASH> 100644
--- a/modules/phenyl-http-rules/src/decode-request.js
+++ b/modules/phenyl-http-rules/src/decode-request.js
@@ -30,8 +30,9 @@ export default function decodeRequest(request: EncodedHttpRequest): [RequestData
     case 'DELETE':
       reqData = decodeDELETERequest(request)
       break
+    default:
+      throw new Error(`Could not handle HTTP method: ${request.method}. Only GET|POST|PUT|DELETE are allowed.`)
   }
-  // $FlowIssue(reqData-is-always-initialized)
   return [reqData, sessionId]
 }
[phenyl-http-rules] throw error when unknown HTTP method is given