diff --git a/protocol/chainsync/client.go b/protocol/chainsync/client.go
index 0ceb1d77..e48beec2 100644
--- a/protocol/chainsync/client.go
+++ b/protocol/chainsync/client.go
@@ -447,6 +447,7 @@ func (c *Client) syncLoop() {
 		msg := NewMsgRequestNext()
 		if err := c.SendMessage(msg); err != nil {
 			c.SendError(err)
+			c.busyMutex.Unlock()
 			return
 		}
 		c.busyMutex.Unlock()