diff --git a/src/dns/nm-dns-manager.c b/src/dns/nm-dns-manager.c
index 4315cdc301..80ce750da8 100644
--- a/src/dns/nm-dns-manager.c
+++ b/src/dns/nm-dns-manager.c
@@ -1320,6 +1320,7 @@ rebuild_domain_lists (NMDnsManager *self)
 	gs_unref_hashtable GHashTable *ht = NULL;
 	gs_unref_hashtable GHashTable *wildcard_entries = NULL;
 	CList *head;
+	int prev_priority = G_MININT;
 
 	head = _ip_config_lst_head (self);
 	c_list_for_each_entry (ip_data, head, ip_config_lst) {
@@ -1369,7 +1370,10 @@ rebuild_domain_lists (NMDnsManager *self)
 		n_domains = nm_ip_config_get_num_domains (ip_config);
 
 		priority = nm_ip_config_get_dns_priority (ip_config);
+
 		nm_assert (priority != 0);
+		nm_assert (prev_priority <= priority);
+		prev_priority = priority;
 
 		cap_dom = 2u + NM_MAX (n_domains, n_searches);