diff --git a/js/xpconnect/src/Sandbox.cpp b/js/xpconnect/src/Sandbox.cpp
index c3b740e7e5..9e46f2dae0 100644
--- a/js/xpconnect/src/Sandbox.cpp
+++ b/js/xpconnect/src/Sandbox.cpp
@@ -352,8 +352,6 @@ static bool SandboxStructuredClone(JSContext* cx, unsigned argc, Value* vp) {
     return false;
   }
 
-  MOZ_ASSERT_IF(result.isGCThing(),
-                !JS::GCThingIsMarkedGray(result.toGCCellPtr()));
   args.rval().set(result);
   return true;
 }