diff --git a/apps/emqx_replay/src/emqx_replay_message_storage.erl b/apps/emqx_replay/src/emqx_replay_message_storage.erl
index f58c006cd..d14a07c6d 100644
--- a/apps/emqx_replay/src/emqx_replay_message_storage.erl
+++ b/apps/emqx_replay/src/emqx_replay_message_storage.erl
@@ -105,7 +105,7 @@
 %% Debug/troubleshooting:
 %% Keymappers
 -export([
-    bitsize/1,
+    keymapper_info/1,
     compute_bitstring/3,
     compute_topic_bitmask/2,
     compute_time_bitmask/1,
@@ -390,9 +390,9 @@ refresh_iterator(It = #it{handle = Handle, cursor = Cursor, next_action = Action
 %% Internal exports
 %%================================================================================
 
--spec bitsize(keymapper()) -> bits().
-bitsize(#keymapper{bitsize = Bitsize}) ->
-    Bitsize.
+-spec keymapper_info(keymapper()) -> [bitsource()].
+keymapper_info(#keymapper{source = Source, bitsize = Bitsize, epoch = Epoch}) ->
+    #{source => Source, bitsize => Bitsize, epoch => Epoch}.
 
 make_message_key(Topic, PublishedAt, MessageID, Keymapper) ->
     combine(compute_bitstring(Topic, PublishedAt, Keymapper), MessageID, Keymapper).
diff --git a/apps/emqx_replay/test/props/prop_replay_message_storage.erl b/apps/emqx_replay/test/props/prop_replay_message_storage.erl
index 20c897c2a..c468097c7 100644
--- a/apps/emqx_replay/test/props/prop_replay_message_storage.erl
+++ b/apps/emqx_replay/test/props/prop_replay_message_storage.erl
@@ -28,13 +28,14 @@
 %%--------------------------------------------------------------------
 
 prop_bitstring_computes() ->
-    ?FORALL(Keymapper, keymapper(), begin
-        Bitsize = emqx_replay_message_storage:bitsize(Keymapper),
+    ?FORALL(
+        Keymapper,
+        keymapper(),
         ?FORALL({Topic, Timestamp}, {topic(), integer()}, begin
             BS = emqx_replay_message_storage:compute_bitstring(Topic, Timestamp, Keymapper),
-            is_integer(BS) andalso (BS < (1 bsl Bitsize))
+            is_integer(BS) andalso (BS < (1 bsl get_keymapper_bitsize(Keymapper)))
         end)
-    end).
+    ).
 
 prop_topic_bitmask_computes() ->
     Keymapper = make_keymapper(16, [8, 12, 16], 100),
@@ -56,7 +57,7 @@ prop_next_seek_monotonic() ->
             ),
             ?FORALL(
                 Bitstring,
-                bitstr(emqx_replay_message_storage:bitsize(Keymapper)),
+                bitstr(get_keymapper_bitsize(Keymapper)),
                 emqx_replay_message_storage:compute_next_seek(Bitstring, Filter) >= Bitstring
             )
         end
@@ -436,6 +437,9 @@ make_keymapper(TimestampBits, TopicBits, MaxEpoch) ->
         epoch => MaxEpoch
     }).
 
+get_keymapper_bitsize(Keymapper) ->
+    maps:get(bitsize, emqx_replay_message_storage:keymapper_info(Keymapper)).
+
 -spec interleave(list({Tag, list(E)}), rand:state()) -> list({Tag, E}).
 interleave(Seqs, Rng) ->
     interleave(Seqs, length(Seqs), Rng).