diff --git a/src/checks.c b/src/checks.c
index 76bd8e3df..aeb3b79b6 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -1488,12 +1488,16 @@ static struct task *server_warmup(struct task *t, void *context, unsigned short
 	    (s->next_state != SRV_ST_STARTING))
 		return t;
 
+	HA_SPIN_LOCK(SERVER_LOCK, &s->lock);
+
 	/* recalculate the weights and update the state */
 	server_recalc_eweight(s, 1);
 
 	/* probably that we can refill this server with a bit more connections */
 	pendconn_grab_from_px(s);
 
+	HA_SPIN_UNLOCK(SERVER_LOCK, &s->lock);
+
 	/* get back there in 1 second or 1/20th of the slowstart interval,
 	 * whichever is greater, resulting in small 5% steps.
 	 */