diff --git a/apps/emqx_durable_storage/src/emqx_ds_replication_layer_egress.erl b/apps/emqx_durable_storage/src/emqx_ds_replication_layer_egress.erl
index 6d879dbb6..b1a1c0cb4 100644
--- a/apps/emqx_durable_storage/src/emqx_ds_replication_layer_egress.erl
+++ b/apps/emqx_durable_storage/src/emqx_ds_replication_layer_egress.erl
@@ -193,14 +193,6 @@ do_enqueue(From, Sync, MsgOrBatch, S0 = #s{n = N, batch = Batch, pending_replies
             Msg ->
                 S0#s{n = N + 1, batch = [Msg | Batch]}
         end,
-    S2 =
-        case N >= NMax of
-            true ->
-                _ = erlang:cancel_timer(S0#s.tref),
-                do_flush(S1);
-            false ->
-                S1
-        end,
     %% TODO: later we may want to delay the reply until the message is
     %% replicated, but it requies changes to the PUBACK/PUBREC flow to
     %% allow for async replies. For now, we ack when the message is
@@ -208,12 +200,20 @@ do_enqueue(From, Sync, MsgOrBatch, S0 = #s{n = N, batch = Batch, pending_replies
     %%
     %% Otherwise, the client would freeze for at least flush interval,
     %% or until the buffer is filled.
-    S =
+    S2 =
         case Sync of
             true ->
-                S2#s{pending_replies = [From | Replies]};
+                S1#s{pending_replies = [From | Replies]};
             false ->
                 gen_server:reply(From, ok),
+                S1
+        end,
+    S =
+        case N >= NMax of
+            true ->
+                _ = erlang:cancel_timer(S2#s.tref),
+                do_flush(S2);
+            false ->
                 S2
         end,
     %% TODO: add a backpressure mechanism for the server to avoid