--- a/editor/libeditor/EditorEventListener.cpp
+++ b/editor/libeditor/EditorEventListener.cpp
@@ -743,16 +743,19 @@ nsresult EditorEventListener::DragOverOr
 
   if (DetachedFromEditorOrDefaultPrevented(aDragEvent->WidgetEventPtr())) {
     return NS_OK;
   }
 
   int32_t dropOffset = -1;
   nsCOMPtr<nsIContent> dropParentContent =
       aDragEvent->GetRangeParentContentAndOffset(&dropOffset);
+  if (NS_WARN_IF(!dropParentContent)) {
+    return NS_ERROR_FAILURE;
+  }
   if (DetachedFromEditor()) {
     RefuseToDropAndHideCaret(aDragEvent);
     return NS_OK;
   }
 
   bool notEditable = !dropParentContent->IsEditable() ||
                      mEditorBase->IsReadonly() || mEditorBase->IsDisabled();