diff --git a/js/xpconnect/src/Sandbox.cpp b/js/xpconnect/src/Sandbox.cpp
index bd49055c527f..2fac0dc650b1 100644
--- a/js/xpconnect/src/Sandbox.cpp
+++ b/js/xpconnect/src/Sandbox.cpp
@@ -451,6 +451,8 @@ CloneNonReflectors(JSContext *cx, MutableHandleValue val)
         Maybe<JSAutoCompartment> ac;
         if (val.isObject()) {
             ac.construct(cx, &val.toObject());
+        } else if (val.isString() && !JS_WrapValue(cx, val)) {
+            return false;
         }
 
         if (!buffer.write(cx, val,