2 files changed, 16 insertions, 6 deletions
diff --git a/js/src/vm/AsyncFunction.cpp b/js/src/vm/AsyncFunction.cpp
index bd0b4f32a..1e0c7d7c2 100644
--- a/js/src/vm/AsyncFunction.cpp
+++ b/js/src/vm/AsyncFunction.cpp
@@ -107,18 +107,15 @@ WrappedAsyncFunction(JSContext* cx, unsigned argc, Value* vp)
 //  the async function's body, replacing `await` with `yield`.  `wrapped` is a
 // function that is visible to the outside, and handles yielded values.
 JSObject*
-js::WrapAsyncFunction(JSContext* cx, HandleFunction unwrapped)
+js::WrapAsyncFunctionWithProto(JSContext* cx, HandleFunction unwrapped, HandleObject proto)
 {
     MOZ_ASSERT(unwrapped->isStarGenerator());
+    MOZ_ASSERT(proto, "We need an explicit prototype to avoid the default"
+                      "%FunctionPrototype% fallback in NewFunctionWithProto().");
 
     // Create a new function with AsyncFunctionPrototype, reusing the name and
     // the length of `unwrapped`.
 
-    // Step 1.
-    RootedObject proto(cx, GlobalObject::getOrCreateAsyncFunctionPrototype(cx, cx->global()));
-    if (!proto)
-        return nullptr;
-
     RootedAtom funName(cx, unwrapped->name());
     uint16_t length;
     if (!unwrapped->getLength(cx, &length))
@@ -141,6 +138,16 @@ js::WrapAsyncFunction(JSContext* cx, HandleFunction unwrapped)
     return wrapped;
 }
 
+JSObject*
+js::WrapAsyncFunction(JSContext* cx, HandleFunction unwrapped)
+{
+    RootedObject proto(cx, GlobalObject::getOrCreateAsyncFunctionPrototype(cx, cx->global()));
+    if (!proto)
+        return nullptr;
+
+    return WrapAsyncFunctionWithProto(cx, unwrapped, proto);
+}
+
 enum class ResumeKind {
     Normal,
     Throw
diff --git a/js/src/vm/AsyncFunction.h b/js/src/vm/AsyncFunction.h
index ddf81a177..d7f2c1311 100644
--- a/js/src/vm/AsyncFunction.h
+++ b/js/src/vm/AsyncFunction.h
@@ -22,6 +22,9 @@ bool
 IsWrappedAsyncFunction(JSFunction* fun);
 
 JSObject*
+WrapAsyncFunctionWithProto(JSContext* cx, HandleFunction unwrapped, HandleObject proto);
+
+JSObject*
 WrapAsyncFunction(JSContext* cx, HandleFunction unwrapped);
 
 MOZ_MUST_USE bool