1 files changed, 4 insertions, 2 deletions
diff --git a/dom/base/FragmentOrElement.cpp b/dom/base/FragmentOrElement.cpp
index 5755fb8173..e341ae315b 100644
--- a/dom/base/FragmentOrElement.cpp
+++ b/dom/base/FragmentOrElement.cpp
@@ -584,8 +584,10 @@ FragmentOrElement::nsDOMSlots::Traverse(nsCycleCollectionTraversalCallback &cb)
 
   if (mExtendedSlots->mCustomElementData) {
     for (uint32_t i = 0;
-         i < mExtendedSlots->mCustomElementData->mCallbackQueue.Length(); i++) {
-      mExtendedSlots->mCustomElementData->mCallbackQueue[i]->Traverse(cb);
+         i < mExtendedSlots->mCustomElementData->mReactionQueue.Length(); i++) {
+      if (mExtendedSlots->mCustomElementData->mReactionQueue[i]) {
+        mExtendedSlots->mCustomElementData->mReactionQueue[i]->Traverse(cb);
+      }
     }
   }