--- a/js/src/builtin/streams/WritableStream.cpp
+++ b/js/src/builtin/streams/WritableStream.cpp
@@ -175,21 +175,22 @@ static bool WritableStream_locked(JSCont
 }
 
 /**
  * Streams spec, 4.2.5.2. abort(reason)
  */
 static bool WritableStream_abort(JSContext* cx, unsigned argc, Value* vp) {
   CallArgs args = CallArgsFromVp(argc, vp);
 
-  // Step 1: If ! WritableStream(this) is false, throw a TypeError exception.
+  // Step 1: If ! IsWritableStream(this) is false, return a promise rejected
+  //         with a TypeError exception.
   Rooted<WritableStream*> unwrappedStream(
       cx, UnwrapAndTypeCheckThis<WritableStream>(cx, args, "abort"));
   if (!unwrappedStream) {
-    return false;
+    return ReturnPromiseRejectedWithPendingError(cx, args);
   }
 
   // Step 2: If ! IsWritableStreamLocked(this) is true, return a promise
   //         rejected with a TypeError exception.
   if (unwrappedStream->isLocked()) {
     JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
                               JSMSG_CANT_USE_LOCKED_WRITABLESTREAM, "abort");
     return ReturnPromiseRejectedWithPendingError(cx, args);