diff --git a/packages/server-shared/src/types/websocket/events.ts b/packages/server-shared/src/types/websocket/events.ts
index 0125e29b9..266865f00 100644
--- a/packages/server-shared/src/types/websocket/events.ts
+++ b/packages/server-shared/src/types/websocket/events.ts
@@ -166,7 +166,7 @@ export interface WebSocketBaseEvent<T, D, S extends string = string> {
   /**
    * @deprecated Prefer metadata.source.
    */
-  source: WebSocketEventSource | S
+  source?: WebSocketEventSource | S
   metadata?: {
     source: MetadataEventSource
   }