diff --git a/src/log.c b/src/log.c
index ed45a73a1..b2e6231fa 100644
--- a/src/log.c
+++ b/src/log.c
@@ -1672,8 +1672,15 @@ send:
 	iovec[7].iov_len  = 1;
 
 	if (logsrv->addr.ss_family == AF_UNSPEC) {
-		/* the target is a direct file descriptor */
+		/* the target is a direct file descriptor. While writev() guarantees
+		 * to write everything, it doesn't guarantee that it will not be
+		 * interrupted while doing so. This occasionally results in interleaved
+		 * messages when the output is a tty, hence the lock. There's no real
+		 * performance concern here for such type of output.
+		 */
+		HA_SPIN_LOCK(LOGSRV_LOCK, &logsrv->lock);
 		sent = writev(*plogfd, iovec, 8);
+		HA_SPIN_UNLOCK(LOGSRV_LOCK, &logsrv->lock);
 	}
 	else {
 		msghdr.msg_name = (struct sockaddr *)&logsrv->addr;