diff --git a/src/idle.c b/src/idle.c
index e3b16c856c..7ea0cd15de 100644
--- a/src/idle.c
+++ b/src/idle.c
@@ -241,7 +241,6 @@ static void rt_defunct_execute(void)
     }
 }
 
-extern void rt_system_power_manager(void);
 static void rt_thread_idle_entry(void *parameter)
 {
 #ifdef RT_USING_SMP
@@ -275,6 +274,7 @@ static void rt_thread_idle_entry(void *parameter)
 #endif /* RT_USING_SMP */
 
 #ifdef RT_USING_PM
+        void rt_system_power_manager(void);
         rt_system_power_manager();
 #endif /* RT_USING_PM */
     }