diff --git a/serversession-backend-acid-state/src/Web/ServerSession/Backend/Acid/Internal.hs b/serversession-backend-acid-state/src/Web/ServerSession/Backend/Acid/Internal.hs
index 12ae658..81df8a1 100644
--- a/serversession-backend-acid-state/src/Web/ServerSession/Backend/Acid/Internal.hs
+++ b/serversession-backend-acid-state/src/Web/ServerSession/Backend/Acid/Internal.hs
@@ -139,7 +139,7 @@ replaceSession :: SS.Session -> Update ServerSessionAcidState ()
 replaceSession session = do
   -- Check that the old session exists while replacing it.
   ServerSessionAcidState sits aits <- get
-  let (moldSession, sits') = M.updateLookupWithKey (\_ _ -> Just session) sid sits
+  let (moldSession, sits') = M.insertLookupWithKey (\_ v _ -> v) sid session sits
       sid = SS.sessionKey session
   case moldSession of
     Nothing -> E.throw $ SS.SessionDoesNotExist session
diff --git a/serversession/tests/Main.hs b/serversession/tests/Main.hs
index 095647b..789d925 100644
--- a/serversession/tests/Main.hs
+++ b/serversession/tests/Main.hs
@@ -307,7 +307,7 @@ instance Storage MockStorage where
   replaceSession sto session =
     join $ I.atomicModifyIORef' (mockSessions sto) $ \oldMap ->
       let (moldVal, newMap) =
-            M.updateLookupWithKey (\_ _ -> Just session) (sessionKey session) oldMap
+            M.insertLookupWithKey (\_ v _ -> v) (sessionKey session) session oldMap
       in maybe
            (oldMap, E.throwIO $ SessionDoesNotExist session)
            (const (newMap, return ()))