diff --git a/lib/hooks/promote-sidebar.react.js b/lib/hooks/promote-sidebar.react.js
--- a/lib/hooks/promote-sidebar.react.js
+++ b/lib/hooks/promote-sidebar.react.js
@@ -37,7 +37,7 @@
 
   const loadingStatus = useSelector(loadingStatusSelector);
 
-  const parentID = threadInfo ? threadInfo.parentThreadID : parentThreadID;
+  const parentID = threadInfo?.parentThreadID ?? parentThreadID;
   const parentThreadInfo: ?ThreadInfo = useSelector(state =>
     parentID ? threadInfoSelector(state)[parentID] : null,
   );