diff --git a/frontend/views/containers/chatroom/CreatePoll.vue b/frontend/views/containers/chatroom/CreatePoll.vue
index 364c4ae2c..fdc05d80e 100644
--- a/frontend/views/containers/chatroom/CreatePoll.vue
+++ b/frontend/views/containers/chatroom/CreatePoll.vue
@@ -273,6 +273,9 @@ export default {
   height: 0;
   pointer-events: none;
   overflow: hidden;
+  // NOTE: z-index should be bigger than the one of sidebar
+  //       because CreatePool modal is rendered before the sidebar
+  // REF:  https://github.com/okTurtles/group-income/issues/1843
   z-index: $zindex-modal + 1;
 
   &.is-active {