diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 7a9d4d7358f..898bb9fe490 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -592,9 +592,9 @@ unsafe impl<U> JSTraceable for TypedSize2D<f32, U> {
     }
 }
 
-unsafe impl<T: JSTraceable> JSTraceable for Mutex<T> {
-    unsafe fn trace(&self, trc: *mut JSTracer) {
-        self.lock().unwrap().trace(trc);
+unsafe impl JSTraceable for Mutex<Option<SharedRt>> {
+    unsafe fn trace(&self, _trc: *mut JSTracer) {
+        // Do nothing.
     }
 }