diff --git a/src/apps/mdns/mdns.c b/src/apps/mdns/mdns.c
index 8597103b..c5b68791 100644
--- a/src/apps/mdns/mdns.c
+++ b/src/apps/mdns/mdns.c
@@ -103,7 +103,7 @@ static const ip_addr_t v6group = DNS_MQUERY_IPV6_GROUP_INIT;
 static u8_t mdns_netif_client_id;
 static struct udp_pcb *mdns_pcb;
 NETIF_DECLARE_EXT_CALLBACK(netif_callback)
-static mdns_name_result_cb_t mdns_name_result_cb = NULL;
+static mdns_name_result_cb_t mdns_name_result_cb;
 
 #define NETIF_TO_HOST(netif) (struct mdns_host*)(netif_get_client_data(netif, mdns_netif_client_id))
 
@@ -1830,7 +1830,7 @@ mdns_handle_response(struct mdns_packet *pkt)
       if (conflict != 0) {
         sys_untimeout(mdns_probe, pkt->netif);
         if (mdns_name_result_cb != NULL) {
-          mdns_name_result_cb(pkt->netif, 0);
+          mdns_name_result_cb(pkt->netif, MDNS_PROBING_CONFLICT);
         }
       }
     }
@@ -2018,7 +2018,7 @@ mdns_probe(void* arg)
     mdns->probing_state = MDNS_PROBING_COMPLETE;
     mdns_resp_announce(netif);
     if (mdns_name_result_cb != NULL) {
-      mdns_name_result_cb(netif, 1);
+      mdns_name_result_cb(netif, MDNS_PROBING_SUCCESSFUL);
     }
   } else {
 #if LWIP_IPV4
@@ -2331,6 +2331,8 @@ mdns_resp_announce(struct netif *netif)
   } /* else: ip address changed while probing was ongoing? todo reset counter to restart? */
 }
 
+/** Register a callback function that is called if probing is completed successfully
+ * or with a conflict. */
 void
 mdns_resp_register_name_result_cb(mdns_name_result_cb_t cb)
 {
diff --git a/src/include/lwip/apps/mdns.h b/src/include/lwip/apps/mdns.h
index b36b81f3..32df511a 100644
--- a/src/include/lwip/apps/mdns.h
+++ b/src/include/lwip/apps/mdns.h
@@ -48,6 +48,9 @@ enum mdns_sd_proto {
   DNSSD_PROTO_TCP = 1
 };
 
+#define MDNS_PROBING_CONFLICT   0
+#define MDNS_PROBING_SUCCESSFUL 1
+
 #define MDNS_LABEL_MAXLEN  63
 
 struct mdns_host;
@@ -57,9 +60,9 @@ struct mdns_service;
 typedef void (*service_get_txt_fn_t)(struct mdns_service *service, void *txt_userdata);
 
 /** Callback function to let application know the result of probing network for name
- *  uniqueness, called with result 1 if no other node claimed use for the name for the
- *  netif or a service and is safe to use, or 0 if another node is already using it and
- *  mdns is disabled on this interface */
+ * uniqueness, called with result MDNS_PROBING_SUCCESSFUL if no other node claimed
+ * use for the name for the netif or a service and is safe to use, or MDNS_PROBING_CONFLICT
+ * if another node is already using it and mdns is disabled on this interface */
 typedef void (*mdns_name_result_cb_t)(struct netif* netif, u8_t result);
 
 void mdns_resp_init(void);