diff --git a/src/core/dns.c b/src/core/dns.c
index 21170cf..ab8ab58 100644
--- a/src/core/dns.c
+++ b/src/core/dns.c
@@ -949,11 +949,19 @@ dns_check_entry(u8_t i)
         /* wait longer for the next retry */
         entry->tmr = entry->retries;
 
-        /* send DNS packet for this entry */
-        err = dns_send(entry);
-        if (err != ERR_OK) {
-          LWIP_DEBUGF(DNS_DEBUG | LWIP_DBG_LEVEL_WARNING,
-                      ("dns_send returned error: %s\n", lwip_strerr(err)));
+        if (!ip_addr_isany(&dns_servers[entry->server_idx])) {
+          /* send DNS packet for this entry */
+          err = dns_send(entry);
+          if (err != ERR_OK) {
+            LWIP_DEBUGF(DNS_DEBUG | LWIP_DBG_LEVEL_WARNING,
+                        ("dns_send returned error: %s\n", lwip_strerr(err)));
+          }
+        } else {
+          /* DNS server not valid anymore, e.g. PPP netif has been shut down */
+          /* call specified callback function if provided */
+          dns_call_found(i, NULL);
+          /* flush this entry */
+          entry->state = DNS_STATE_UNUSED;
         }
       }
       break;
@@ -1313,8 +1321,15 @@ dns_gethostbyname(const char *hostname, ip_addr_t *addr, dns_found_callback foun
     return ERR_OK;
   }
 
-  /* queue query with specified callback */
-  return dns_enqueue(hostname, hostnamelen, found, callback_arg);
+  if (!ip_addr_isany_val(dns_servers[0])) {
+    /* queue query with specified callback */
+    return dns_enqueue(hostname, hostnamelen, found, callback_arg);
+  } else {
+    /* No (primary) DNS server available */
+    /* @todo: IPv6 support... */
+    ip_addr_set_any(0, addr);
+    return ERR_OK;
+  }
 }
 
 #endif /* LWIP_DNS */