diff --git a/include/mqtt_client.h b/include/mqtt_client.h
index 348d072..5d8c8b3 100644
--- a/include/mqtt_client.h
+++ b/include/mqtt_client.h
@@ -375,6 +375,7 @@ esp_err_t esp_mqtt_client_destroy(esp_mqtt_client_handle_t client);
  * @param config    mqtt configuration structure
  *
  * @return ESP_ERR_NO_MEM if failed to allocate
+ *         ESP_ERR_INVALID_ARG if conflicts on transport configuration.
  *         ESP_OK on success
  */
 esp_err_t esp_mqtt_set_config(esp_mqtt_client_handle_t client, const esp_mqtt_client_config_t *config);
diff --git a/mqtt_client.c b/mqtt_client.c
index 6c5b32e..698ae7c 100644
--- a/mqtt_client.c
+++ b/mqtt_client.c
@@ -536,11 +536,11 @@ esp_err_t esp_mqtt_set_config(esp_mqtt_client_handle_t client, const esp_mqtt_cl
             goto _mqtt_set_config_failed;
         }
     }
-    esp_mqtt_check_cfg_conflict(client->config, config);
+    esp_err_t config_has_conflict = esp_mqtt_check_cfg_conflict(client->config, config);
 
     MQTT_API_UNLOCK(client);
 
-    return ESP_OK;
+    return config_has_conflict;
 _mqtt_set_config_failed:
     esp_mqtt_destroy_config(client);
     MQTT_API_UNLOCK(client);