diff --git a/apps/emqx_conf/src/emqx_conf_app.erl b/apps/emqx_conf/src/emqx_conf_app.erl
index 1505b8c3e..f5ecbedb6 100644
--- a/apps/emqx_conf/src/emqx_conf_app.erl
+++ b/apps/emqx_conf/src/emqx_conf_app.erl
@@ -180,17 +180,7 @@ sync_cluster_conf2(Nodes) ->
 
 %% @private Filter out the nodes which are running a newer version than this node.
 sync_cluster_conf3(Ready) ->
-    NotNewer = fun({ok, #{release := RemoteRelease}}) ->
-        try
-            emqx_release:vsn_compare(RemoteRelease) =/= newer
-        catch
-            _:_ ->
-                %% If the version is not valid (without v or e prefix),
-                %% we know it's older than v5.1.0/e5.1.0
-                true
-        end
-    end,
-    case lists:filter(NotNewer, Ready) of
+    case lists:filter(fun is_older_or_same_version/1, Ready) of
         [] ->
             %% All available core nodes are running a newer version than this node.
             %% Start this node without syncing cluster config from them.
@@ -213,6 +203,19 @@ sync_cluster_conf3(Ready) ->
             sync_cluster_conf4(Ready2)
     end.
 
+is_older_or_same_version({ok, #{release := RemoteRelease}}) ->
+    try
+        emqx_release:vsn_compare(RemoteRelease) =/= newer
+    catch
+        _:_ ->
+            %% If the version is not valid (without v or e prefix),
+            %% we know it's older than v5.1.0/e5.1.0
+            true
+    end;
+is_older_or_same_version(_) ->
+    %% older version has no 'release' field
+    true.
+
 %% @private Some core nodes are running and replied with their configs successfully.
 %% Try to sort the results and save the first one for local use.
 sync_cluster_conf4(Ready) ->