diff --git a/packages/aws-appsync-subscription-link/src/subscription-handshake-link.ts b/packages/aws-appsync-subscription-link/src/subscription-handshake-link.ts
index 64d52873..b1dc48c7 100644
--- a/packages/aws-appsync-subscription-link/src/subscription-handshake-link.ts
+++ b/packages/aws-appsync-subscription-link/src/subscription-handshake-link.ts
@@ -51,7 +51,7 @@ export class SubscriptionHandshakeLink extends ApolloLink {
         this.subsInfoContextKey = subsInfoContextKey;
     }
 
-    request(operation: Operation) {
+    request(operation: Operation): Observable<FetchResult> | null {
         const {
             [this.subsInfoContextKey]: subsInfo,
             controlMessages: { [CONTROL_EVENTS_KEY]: controlEvents } = { [CONTROL_EVENTS_KEY]: undefined }