diff --git a/ESP32-IDF_FreeRTOS/I2C_MultiDevice/main/hello_world_main.c b/ESP32-IDF_FreeRTOS/I2C_MultiDevice/main/hello_world_main.c
index 2c704e3c3..2b039ef4d 100644
--- a/ESP32-IDF_FreeRTOS/I2C_MultiDevice/main/hello_world_main.c
+++ b/ESP32-IDF_FreeRTOS/I2C_MultiDevice/main/hello_world_main.c
@@ -18,6 +18,8 @@
 #include "esp_flash.h"
 #include "esp_system.h"
 
+SemaphoreHandle_t xMutex;
+
 void task1(void *pvParameters);
 void task2(void *pvParameters);