diff --git a/src/Simplex/Messaging/Agent.hs b/src/Simplex/Messaging/Agent.hs
index 652e2d58d..dddaa7231 100644
--- a/src/Simplex/Messaging/Agent.hs
+++ b/src/Simplex/Messaging/Agent.hs
@@ -138,6 +138,8 @@ import qualified Data.List.NonEmpty as L
 import Data.Map.Strict (Map)
 import qualified Data.Map.Strict as M
 import Data.Maybe (catMaybes, fromMaybe, isJust, isNothing, mapMaybe)
+import Data.Set (Set)
+import qualified Data.Set as S
 import Data.Text (Text)
 import qualified Data.Text as T
 import Data.Time.Clock
@@ -354,12 +356,12 @@ sendMessage c = withAgentEnv c .:: sendMessage' c
 type MsgReq = (ConnId, PQEncryption, MsgFlags, MsgBody)
 
 -- | Send multiple messages to different connections (SEND command)
-sendMessages :: AgentClient -> [MsgReq] -> IO [Either AgentErrorType (AgentMsgId, PQEncryption)]
-sendMessages c = withAgentEnv' c . sendMessages' c
+sendMessages :: AgentClient -> [MsgReq] -> AE [Either AgentErrorType (AgentMsgId, PQEncryption)]
+sendMessages c = withAgentEnv c . sendMessages' c
 {-# INLINE sendMessages #-}
 
-sendMessagesB :: Traversable t => AgentClient -> t (Either AgentErrorType MsgReq) -> IO (t (Either AgentErrorType (AgentMsgId, PQEncryption)))
-sendMessagesB c = withAgentEnv' c . sendMessagesB' c
+sendMessagesB :: Traversable t => AgentClient -> t (Either AgentErrorType MsgReq) -> AE (t (Either AgentErrorType (AgentMsgId, PQEncryption)))
+sendMessagesB c = withAgentEnv c . sendMessagesB' c
 {-# INLINE sendMessagesB #-}
 
 ackMessage :: AgentClient -> ConnId -> AgentMsgId -> Maybe MsgReceiptInfo -> AE ()
@@ -1033,16 +1035,27 @@ getNotificationMessage' c nonce encNtfInfo = do
 
 -- | Send message to the connection (SEND command) in Reader monad
 sendMessage' :: AgentClient -> ConnId -> PQEncryption -> MsgFlags -> MsgBody -> AM (AgentMsgId, PQEncryption)
-sendMessage' c connId pqEnc msgFlags msg = ExceptT $ runIdentity <$> sendMessagesB' c (Identity (Right (connId, pqEnc, msgFlags, msg)))
+sendMessage' c connId pqEnc msgFlags msg = ExceptT $ runIdentity <$> sendMessagesB_ c (Identity (Right (connId, pqEnc, msgFlags, msg))) (S.singleton connId)
 {-# INLINE sendMessage' #-}
 
 -- | Send multiple messages to different connections (SEND command) in Reader monad
-sendMessages' :: AgentClient -> [MsgReq] -> AM' [Either AgentErrorType (AgentMsgId, PQEncryption)]
+sendMessages' :: AgentClient -> [MsgReq] -> AM [Either AgentErrorType (AgentMsgId, PQEncryption)]
 sendMessages' c = sendMessagesB' c . map Right
 {-# INLINE sendMessages' #-}
 
-sendMessagesB' :: forall t. Traversable t => AgentClient -> t (Either AgentErrorType MsgReq) -> AM' (t (Either AgentErrorType (AgentMsgId, PQEncryption)))
-sendMessagesB' c reqs = withConnLocks c connIds "sendMessages" $ do
+sendMessagesB' :: forall t. Traversable t => AgentClient -> t (Either AgentErrorType MsgReq) -> AM (t (Either AgentErrorType (AgentMsgId, PQEncryption)))
+sendMessagesB' c reqs = do
+  connIds <- liftEither $ foldl' addConnId (Right S.empty) reqs
+  lift $ sendMessagesB_ c reqs connIds
+  where
+    addConnId s@(Right s') (Right (connId, _, _, _))
+      | B.null connId = s
+      | connId `S.notMember` s' = Right $ S.insert connId s'
+      | otherwise = Left $ INTERNAL "sendMessages: duplicate connection ID"
+    addConnId s _ = s
+
+sendMessagesB_ :: forall t. Traversable t => AgentClient -> t (Either AgentErrorType MsgReq) -> Set ConnId -> AM' (t (Either AgentErrorType (AgentMsgId, PQEncryption)))
+sendMessagesB_ c reqs connIds = withConnLocks c connIds "sendMessages" $ do
   reqs' <- withStoreBatch c (\db -> fmap (bindRight $ \req@(connId, _, _, _) -> bimap storeError (req,) <$> getConn db connId) reqs)
   let (toEnable, reqs'') = mapAccumL prepareConn [] reqs'
   void $ withStoreBatch' c $ \db -> map (\connId -> setConnPQSupport db connId PQSupportOn) toEnable
@@ -1064,7 +1077,6 @@ sendMessagesB' c reqs = withConnLocks c connIds "sendMessages" $ do
               let cData' = cData {pqSupport = PQSupportOn} :: ConnData
                in (connId : acc, Right (cData', sqs, Just pqEnc, msgFlags, A_MSG msg))
           | otherwise = (acc, Right (cData, sqs, Just pqEnc, msgFlags, A_MSG msg))
-    connIds = map (\(connId, _, _, _) -> connId) $ rights $ toList reqs
 
 -- / async command processing v v v
 
diff --git a/src/Simplex/Messaging/Agent/Client.hs b/src/Simplex/Messaging/Agent/Client.hs
index e59dee7a1..2dd4ec3c9 100644
--- a/src/Simplex/Messaging/Agent/Client.hs
+++ b/src/Simplex/Messaging/Agent/Client.hs
@@ -826,15 +826,15 @@ withInvLock' :: AgentClient -> ByteString -> String -> AM' a -> AM' a
 withInvLock' AgentClient {invLocks} = withLockMap invLocks
 {-# INLINE withInvLock' #-}
 
-withConnLocks :: AgentClient -> [ConnId] -> String -> AM' a -> AM' a
-withConnLocks AgentClient {connLocks} = withLocksMap_ connLocks . filter (not . B.null)
+withConnLocks :: AgentClient -> Set ConnId -> String -> AM' a -> AM' a
+withConnLocks AgentClient {connLocks} = withLocksMap_ connLocks
 {-# INLINE withConnLocks #-}
 
 withLockMap :: (Ord k, MonadUnliftIO m) => TMap k Lock -> k -> String -> m a -> m a
 withLockMap = withGetLock . getMapLock
 {-# INLINE withLockMap #-}
 
-withLocksMap_ :: (Ord k, MonadUnliftIO m) => TMap k Lock -> [k] -> String -> m a -> m a
+withLocksMap_ :: (Ord k, MonadUnliftIO m) => TMap k Lock -> Set k -> String -> m a -> m a
 withLocksMap_ = withGetLocks . getMapLock
 {-# INLINE withLocksMap_ #-}
 
diff --git a/src/Simplex/Messaging/Agent/Lock.hs b/src/Simplex/Messaging/Agent/Lock.hs
index c0647b844..69b8169e2 100644
--- a/src/Simplex/Messaging/Agent/Lock.hs
+++ b/src/Simplex/Messaging/Agent/Lock.hs
@@ -12,6 +12,8 @@ import Control.Monad (void)
 import Control.Monad.Except (ExceptT (..), runExceptT)
 import Control.Monad.IO.Unlift
 import Data.Functor (($>))
+import Data.Set (Set)
+import qualified Data.Set as S
 import UnliftIO.Async (forConcurrently)
 import qualified UnliftIO.Exception as E
 import UnliftIO.STM
@@ -39,13 +41,11 @@ withGetLock getLock key name a =
     (atomically . takeTMVar)
     (const a)
 
-withGetLocks :: MonadUnliftIO m => (k -> STM Lock) -> [k] -> String -> m a -> m a
+withGetLocks :: MonadUnliftIO m => (k -> STM Lock) -> Set k -> String -> m a -> m a
 withGetLocks getLock keys name = E.bracket holdLocks releaseLocks . const
   where
-    holdLocks = forConcurrently keys $ \key -> atomically $ getPutLock getLock key name
-    -- only this withGetLocks would be holding the locks,
-    -- so it's safe to combine all lock releases into one transaction
-    releaseLocks = atomically . mapM_ takeTMVar
+    holdLocks = forConcurrently (S.toList keys) $ \key -> atomically $ getPutLock getLock key name
+    releaseLocks = mapM_ (atomically . takeTMVar)
 
 -- getLock and putTMVar can be in one transaction on the assumption that getLock doesn't write in case the lock already exists,
 -- and in case it is created and added to some shared resource (we use TMap) it also helps avoid contention for the newly created lock.