diff --git a/src/mux_fcgi.c b/src/mux_fcgi.c
index 9b4827174..fd74b56af 100644
--- a/src/mux_fcgi.c
+++ b/src/mux_fcgi.c
@@ -3140,8 +3140,10 @@ struct task *fcgi_timeout_task(struct task *t, void *context, unsigned int state
 		/* We're about to destroy the connection, so make sure nobody attempts
 		 * to steal it from us.
 		 */
-		if (fconn->conn->flags & CO_FL_LIST_MASK)
+		if (fconn->conn->flags & CO_FL_LIST_MASK) {
 			conn_delete_from_tree(&fconn->conn->hash_node->node);
+			fconn->conn->flags &= ~CO_FL_LIST_MASK;
+		}
 
 		HA_SPIN_UNLOCK(IDLE_CONNS_LOCK, &idle_conns[tid].idle_conns_lock);
 	}
diff --git a/src/mux_h1.c b/src/mux_h1.c
index f9bd1d88b..455f62384 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -3297,8 +3297,10 @@ struct task *h1_timeout_task(struct task *t, void *context, unsigned int state)
 		/* We're about to destroy the connection, so make sure nobody attempts
 		 * to steal it from us.
 		 */
-		if (h1c->conn->flags & CO_FL_LIST_MASK)
+		if (h1c->conn->flags & CO_FL_LIST_MASK) {
 			conn_delete_from_tree(&h1c->conn->hash_node->node);
+			h1c->conn->flags &= ~CO_FL_LIST_MASK;
+		}
 
 		HA_SPIN_UNLOCK(IDLE_CONNS_LOCK, &idle_conns[tid].idle_conns_lock);
 	}
diff --git a/src/mux_h2.c b/src/mux_h2.c
index 4ac7fc5da..293c41447 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -4031,6 +4031,7 @@ static int h2_process(struct h2c *h2c)
 		if (conn->flags & CO_FL_LIST_MASK) {
 			HA_SPIN_LOCK(IDLE_CONNS_LOCK, &idle_conns[tid].idle_conns_lock);
 			conn_delete_from_tree(&conn->hash_node->node);
+			conn->flags &= ~CO_FL_LIST_MASK;
 			HA_SPIN_UNLOCK(IDLE_CONNS_LOCK, &idle_conns[tid].idle_conns_lock);
 		}
 	}
@@ -4039,6 +4040,7 @@ static int h2_process(struct h2c *h2c)
 		if (conn->flags & CO_FL_LIST_MASK) {
 			HA_SPIN_LOCK(IDLE_CONNS_LOCK, &idle_conns[tid].idle_conns_lock);
 			conn_delete_from_tree(&conn->hash_node->node);
+			conn->flags &= ~CO_FL_LIST_MASK;
 			HA_SPIN_UNLOCK(IDLE_CONNS_LOCK, &idle_conns[tid].idle_conns_lock);
 		}
 	}
@@ -4118,8 +4120,10 @@ struct task *h2_timeout_task(struct task *t, void *context, unsigned int state)
 		/* We're about to destroy the connection, so make sure nobody attempts
 		 * to steal it from us.
 		 */
-		if (h2c->conn->flags & CO_FL_LIST_MASK)
+		if (h2c->conn->flags & CO_FL_LIST_MASK) {
 			conn_delete_from_tree(&h2c->conn->hash_node->node);
+			h2c->conn->flags &= ~CO_FL_LIST_MASK;
+		}
 
 		HA_SPIN_UNLOCK(IDLE_CONNS_LOCK, &idle_conns[tid].idle_conns_lock);
 	}
@@ -4172,6 +4176,7 @@ do_leave:
 	if (h2c->conn->flags & CO_FL_LIST_MASK) {
 		HA_SPIN_LOCK(IDLE_CONNS_LOCK, &idle_conns[tid].idle_conns_lock);
 		conn_delete_from_tree(&h2c->conn->hash_node->node);
+		h2c->conn->flags &= ~CO_FL_LIST_MASK;
 		HA_SPIN_UNLOCK(IDLE_CONNS_LOCK, &idle_conns[tid].idle_conns_lock);
 	}
 
diff --git a/src/server.c b/src/server.c
index 6e9d5113f..45fc33fa3 100644
--- a/src/server.c
+++ b/src/server.c
@@ -5828,6 +5828,7 @@ static int srv_migrate_conns_to_remove(struct eb_root *idle_tree, struct mt_list
 
 		hash_node = ebmb_entry(node, struct conn_hash_node, node);
 		eb_delete(node);
+		hash_node->conn->flags &= ~CO_FL_LIST_MASK;
 		MT_LIST_APPEND(toremove_list, &hash_node->conn->toremove_list);
 		i++;
 
@@ -5885,6 +5886,7 @@ void srv_release_conn(struct server *srv, struct connection *conn)
 	/* Remove the connection from any tree (safe, idle or available) */
 	HA_SPIN_LOCK(IDLE_CONNS_LOCK, &idle_conns[tid].idle_conns_lock);
 	conn_delete_from_tree(&conn->hash_node->node);
+	conn->flags &= ~CO_FL_LIST_MASK;
 	HA_SPIN_UNLOCK(IDLE_CONNS_LOCK, &idle_conns[tid].idle_conns_lock);
 }