diff --git a/src/_shims/fetch.js b/src/_shims/fetch.js
index 28637363..3c3821fd 100644
--- a/src/_shims/fetch.js
+++ b/src/_shims/fetch.js
@@ -10,4 +10,4 @@ exports.Request = Request;
 exports.Response = Response;
 exports.Headers = Headers;
 
-exports.isPolyfilled = true;
+exports.isPolyfilled = false;