diff --git a/js/src/builtin/streams/ReadableStreamOperations.cpp b/js/src/builtin/streams/ReadableStreamOperations.cpp
index 68088c5a96fa..58ea3fda5714 100644
--- a/js/src/builtin/streams/ReadableStreamOperations.cpp
+++ b/js/src/builtin/streams/ReadableStreamOperations.cpp
@@ -612,11 +612,12 @@ MOZ_MUST_USE bool js::ReadableStreamTee(
  *      ReadableStreamPipeTo ( source, dest, preventClose, preventAbort,
  *                             preventCancel, signal )
  */
-JSObject* js::ReadableStreamPipeTo(JSContext* cx,
-                                   Handle<ReadableStream*> unwrappedSource,
-                                   Handle<WritableStream*> unwrappedDest,
-                                   bool preventClose, bool preventAbort,
-                                   bool preventCancel, Handle<Value> signal) {
+PromiseObject* js::ReadableStreamPipeTo(JSContext* cx,
+                                        Handle<ReadableStream*> unwrappedSource,
+                                        Handle<WritableStream*> unwrappedDest,
+                                        bool preventClose, bool preventAbort,
+                                        bool preventCancel,
+                                        Handle<Value> signal) {
   JS_ReportErrorASCII(cx, "XXX ceci n'est pas une pipe");
   return nullptr;
 }
diff --git a/js/src/builtin/streams/ReadableStreamOperations.h b/js/src/builtin/streams/ReadableStreamOperations.h
index a8c692ee0e76..38cf94020160 100644
--- a/js/src/builtin/streams/ReadableStreamOperations.h
+++ b/js/src/builtin/streams/ReadableStreamOperations.h
@@ -35,7 +35,7 @@ extern MOZ_MUST_USE bool ReadableStreamTee(
     bool cloneForBranch2, JS::MutableHandle<ReadableStream*> branch1Stream,
     JS::MutableHandle<ReadableStream*> branch2Stream);
 
-extern MOZ_MUST_USE JSObject* ReadableStreamPipeTo(
+extern MOZ_MUST_USE PromiseObject* ReadableStreamPipeTo(
     JSContext* cx, JS::Handle<ReadableStream*> unwrappedSource,
     JS::Handle<WritableStream*> unwrappedDest, bool preventClose,
     bool preventAbort, bool preventCancel, JS::Handle<JS::Value> signal);