--- a/dom/media/gmp/GMPCDMCallbackProxy.cpp
+++ b/dom/media/gmp/GMPCDMCallbackProxy.cpp
@@ -152,17 +152,16 @@ public:
   }
 
   NS_IMETHOD Run() override {
     mProxy->OnSessionMessage(mSid, mMsgType, mMsg);
     return NS_OK;
   }
 
   RefPtr<CDMProxy> mProxy;
-  dom::PromiseId mPid;
   nsString mSid;
   dom::MediaKeyMessageType mMsgType;
   nsTArray<uint8_t> mMsg;
 };
 
 void
 GMPCDMCallbackProxy::SessionMessage(const nsCString& aSessionId,
                                     dom::MediaKeyMessageType aMessageType,