diff --git a/apps/emqx_machine/src/emqx_machine_app.erl b/apps/emqx_machine/src/emqx_machine_app.erl
index bae1cecdf..ae837db2c 100644
--- a/apps/emqx_machine/src/emqx_machine_app.erl
+++ b/apps/emqx_machine/src/emqx_machine_app.erl
@@ -24,7 +24,7 @@
 
 start(_Type, _Args) ->
     ok = emqx_machine:start(),
-    emqx_restricted_shell:set_prompt_func(),
+    _ = emqx_restricted_shell:set_prompt_func(),
     emqx_machine_sup:start_link().
 
 stop(_State) ->