diff --git a/ext/src/global.d.ts b/ext/src/global.d.ts
index 38f3c04..5d23f8b 100644
--- a/ext/src/global.d.ts
+++ b/ext/src/global.d.ts
@@ -54,6 +54,12 @@ declare namespace browser.events {
 declare namespace browser.runtime {
     interface Port {
         error: { message: string };
+
+        /**
+         * https://git.io/fjmzb
+         * addListener cb `() => void` is wrong
+         */
+        onMessage: browser.events.Event
     }
 
     function connect (connectInfo: {