diff --git a/examples/nanocoap_server/coap_handler.c b/examples/nanocoap_server/coap_handler.c
index 86dd39993997..2014d302b53a 100644
--- a/examples/nanocoap_server/coap_handler.c
+++ b/examples/nanocoap_server/coap_handler.c
@@ -252,6 +252,9 @@ static ssize_t _time_handler(coap_pkt_t *pkt, uint8_t *buf, size_t len, coap_req
         if (nanocoap_register_observer(context, pkt) == 0) {
             registered = true;
         }
+        else {
+            puts("_time_handler: can't register observer");
+        }
         break;
     case 1:
         /* unregister */