diff --git a/apps/emqx_replay/src/emqx_replay_message_storage.erl b/apps/emqx_replay/src/emqx_replay_message_storage.erl
index dd6c41598..f2a6afaa6 100644
--- a/apps/emqx_replay/src/emqx_replay_message_storage.erl
+++ b/apps/emqx_replay/src/emqx_replay_message_storage.erl
@@ -396,7 +396,8 @@ refresh_iterator(It = #it{handle = Handle, cursor = Cursor, next_action = Action
 %% Internal exports
 %%================================================================================
 
--spec keymapper_info(keymapper()) -> [bitsource()].
+-spec keymapper_info(keymapper()) ->
+    #{source := [bitsource()], bitsize := bits(), epoch := time()}.
 keymapper_info(#keymapper{source = Source, bitsize = Bitsize, epoch = Epoch}) ->
     #{source => Source, bitsize => Bitsize, epoch => Epoch}.