diff --git a/dom/base/nsContentList.h b/dom/base/nsContentList.h
index 90cb25334873..4798d10eb5d3 100644
--- a/dom/base/nsContentList.h
+++ b/dom/base/nsContentList.h
@@ -52,10 +52,13 @@ class nsBaseContentList : public nsINodeList {
   NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS(nsBaseContentList)
 
   void AppendElement(nsIContent* aContent) {
+    MOZ_ASSERT(aContent);
     mElements.AppendElement(aContent);
   }
   void MaybeAppendElement(nsIContent* aContent) {
-    if (aContent) AppendElement(aContent);
+    if (aContent) {
+      AppendElement(aContent);
+    }
   }
 
   /**
diff --git a/layout/inspector/InspectorUtils.cpp b/layout/inspector/InspectorUtils.cpp
index 57f4bb583e7d..95abea8f3561 100644
--- a/layout/inspector/InspectorUtils.cpp
+++ b/layout/inspector/InspectorUtils.cpp
@@ -769,7 +769,7 @@ static void AddOverflowingChildrenOfElement(const nsIFrame* aFrame,
 
       if (FrameHasSpecifiedSize(child) &&
           IsFrameOutsideOfAncestor(child, aAncestorFrame, aRect)) {
-        aList.AppendElement(child->GetContent());
+        aList.MaybeAppendElement(child->GetContent());
         continue;
       }
 
@@ -780,7 +780,7 @@ static void AddOverflowingChildrenOfElement(const nsIFrame* aFrame,
       // calling AddOverflowingChildrenOfElement on it.
       if (currListLength == aList.Length() &&
           IsFrameOutsideOfAncestor(child, aAncestorFrame, aRect)) {
-        aList.AppendElement(child->GetContent());
+        aList.MaybeAppendElement(child->GetContent());
       }
     }
   }