diff --git a/src/backend.c b/src/backend.c
index ba642d958..34e5e7aac 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -1593,8 +1593,11 @@ int connect_server(struct stream *s)
 		s->flags |= SF_CURR_SESS;
 		count = _HA_ATOMIC_ADD(&srv->cur_sess, 1);
 		HA_ATOMIC_UPDATE_MAX(&srv->counters.cur_sess_max, count);
-		if (s->be->lbprm.server_take_conn)
+		if (s->be->lbprm.server_take_conn) {
+			HA_SPIN_LOCK(SERVER_LOCK, &srv->lock);
 			s->be->lbprm.server_take_conn(srv);
+			HA_SPIN_UNLOCK(SERVER_LOCK, &srv->lock);
+		}
 	}
 
 	/* Now handle synchronously connected sockets. We know the stream-int
diff --git a/src/stream.c b/src/stream.c
index bcb9acf78..8d6bdb26c 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -2503,8 +2503,11 @@ void sess_change_server(struct stream *sess, struct server *newsrv)
 		_HA_ATOMIC_SUB(&sess->srv_conn->served, 1);
 		_HA_ATOMIC_SUB(&sess->srv_conn->proxy->served, 1);
 		__ha_barrier_atomic_store();
-		if (sess->srv_conn->proxy->lbprm.server_drop_conn)
+		if (sess->srv_conn->proxy->lbprm.server_drop_conn) {
+			HA_SPIN_LOCK(SERVER_LOCK, &sess->srv_conn->lock);
 			sess->srv_conn->proxy->lbprm.server_drop_conn(sess->srv_conn);
+			HA_SPIN_UNLOCK(SERVER_LOCK, &sess->srv_conn->lock);
+		}
 		stream_del_srv_conn(sess);
 	}
 
@@ -2512,8 +2515,11 @@ void sess_change_server(struct stream *sess, struct server *newsrv)
 		_HA_ATOMIC_ADD(&newsrv->served, 1);
 		_HA_ATOMIC_ADD(&newsrv->proxy->served, 1);
 		__ha_barrier_atomic_store();
-		if (newsrv->proxy->lbprm.server_take_conn)
+		if (newsrv->proxy->lbprm.server_take_conn) {
+			HA_SPIN_LOCK(SERVER_LOCK, &newsrv->lock);
 			newsrv->proxy->lbprm.server_take_conn(newsrv);
+			HA_SPIN_UNLOCK(SERVER_LOCK, &newsrv->lock);
+		}
 		stream_add_srv_conn(sess, newsrv);
 	}
 }