diff --git a/apps/emqx_coap/src/emqx_coap_mqtt_adapter.erl b/apps/emqx_coap/src/emqx_coap_mqtt_adapter.erl
index fb1e6816c..d465f9ca3 100644
--- a/apps/emqx_coap/src/emqx_coap_mqtt_adapter.erl
+++ b/apps/emqx_coap/src/emqx_coap_mqtt_adapter.erl
@@ -105,8 +105,8 @@ call(Pid, Msg, _) ->
 %%--------------------------------------------------------------------
 
 init({ClientId, Username, Password, Channel}) ->
-    ?LOG(debug, "try to start adapter ClientId=~p, Username=~p, Password=~p, Channel=~p",
-         [ClientId, Username, Password, Channel]),
+    ?LOG(debug, "try to start adapter ClientId=~p, Username=~p, Password=~p, "
+                "Channel=~0p", [ClientId, Username, Password, Channel]),
     State0 = #state{peername = Channel,
                     clientid = ClientId,
                     username = Username,