diff --git a/src/client/sse.ts b/src/client/sse.ts
index 5ca724b1..808aa24b 100644
--- a/src/client/sse.ts
+++ b/src/client/sse.ts
@@ -126,7 +126,7 @@ export class SSEClientTransport implements Transport {
   }
 
   private _startOrAuth(): Promise<void> {
-    const fetchImpl = (this?._eventSourceInit?.fetch || this._fetch || fetch) as typeof fetch
+const fetchImpl = (this?._eventSourceInit?.fetch ?? this._fetch ?? fetch) as typeof fetch
     return new Promise((resolve, reject) => {
       this._eventSource = new EventSource(
         this._url.href,