diff --git a/src/Simplex/Messaging/Agent.hs b/src/Simplex/Messaging/Agent.hs
index 195c93833..e3b1bccf4 100644
--- a/src/Simplex/Messaging/Agent.hs
+++ b/src/Simplex/Messaging/Agent.hs
@@ -2307,12 +2307,27 @@ processSMPTransmission c@AgentClient {smpClients, subQ} (tSess@(_, srv, _), v, s
                 unless exists $ addProcessedRatchetKeyHash db connId rkHashRcv
                 pure exists
               getSendRatchetKeys :: m (C.PrivateKeyX448, C.PrivateKeyX448, C.PublicKeyX448, C.PublicKeyX448)
-              getSendRatchetKeys
-                | rss == RSStarted = withStore c (`getRatchetX3dhKeys'` connId)
-                | otherwise = do
+              getSendRatchetKeys = case rss of
+                RSOk -> sendReplyKey -- receiving client
+                RSAllowed -> sendReplyKey
+                RSRequired -> sendReplyKey
+                RSStarted -> withStore c (`getRatchetX3dhKeys'` connId) -- initiating client
+                RSAgreed -> do
+                  withStore' c $ \db -> setConnRatchetSync db connId RSRequired
+                  notifyRatchetSyncError
+                  -- can communicate for other client to reset to RSRequired
+                  -- - need to add new AgentMsgEnvelope, AgentMessage, AgentMessageType
+                  -- - need to deduplicate on receiving side
+                  throwError $ AGENT (A_CRYPTO RATCHET_SYNC)
+                where
+                  sendReplyKey = do
                     (pk1, pk2, e2eParams@(CR.E2ERatchetParams _ k1 k2)) <- liftIO . CR.generateE2EParams $ version e2eOtherPartyParams
                     void $ enqueueRatchetKeyMsgs c cData' sqs e2eParams
                     pure (pk1, pk2, k1, k2)
+                  notifyRatchetSyncError = do
+                    let cData'' = cData' {ratchetSyncState = RSRequired} :: ConnData
+                        conn'' = updateConnection cData'' conn'
+                    notify $ RSYNC RSRequired (Just RATCHET_SYNC) (connectionStats conn'')
               notifyAgreed :: m ()
               notifyAgreed = do
                 let cData'' = cData' {ratchetSyncState = RSAgreed} :: ConnData
diff --git a/src/Simplex/Messaging/Agent/Protocol.hs b/src/Simplex/Messaging/Agent/Protocol.hs
index c4058b75a..efe75e2f5 100644
--- a/src/Simplex/Messaging/Agent/Protocol.hs
+++ b/src/Simplex/Messaging/Agent/Protocol.hs
@@ -1504,6 +1504,8 @@ data AgentCryptoError
     RATCHET_EARLIER Word32
   | -- | too many skipped messages
     RATCHET_SKIPPED Word32
+  | -- | ratchet synchronization error
+    RATCHET_SYNC
   deriving (Eq, Read, Show, Exception)
 
 instance StrEncoding AgentCryptoError where
@@ -1513,12 +1515,14 @@ instance StrEncoding AgentCryptoError where
       <|> "RATCHET_HEADER" $> RATCHET_HEADER
       <|> "RATCHET_EARLIER " *> (RATCHET_EARLIER <$> strP)
       <|> "RATCHET_SKIPPED " *> (RATCHET_SKIPPED <$> strP)
+      <|> "RATCHET_SYNC" $> RATCHET_SYNC
   strEncode = \case
     DECRYPT_AES -> "DECRYPT_AES"
     DECRYPT_CB -> "DECRYPT_CB"
     RATCHET_HEADER -> "RATCHET_HEADER"
     RATCHET_EARLIER n -> "RATCHET_EARLIER " <> strEncode n
     RATCHET_SKIPPED n -> "RATCHET_SKIPPED " <> strEncode n
+    RATCHET_SYNC -> "RATCHET_SYNC"
 
 instance StrEncoding AgentErrorType where
   strP =
@@ -1563,6 +1567,7 @@ cryptoErrToSyncState = \case
   RATCHET_HEADER -> RSRequired
   RATCHET_EARLIER _ -> RSAllowed
   RATCHET_SKIPPED _ -> RSRequired
+  RATCHET_SYNC -> RSRequired
 
 -- | SMP agent command and response parser for commands passed via network (only parses binary length)
 networkCommandP :: Parser ACmd