diff --git a/src/clock.c b/src/clock.c
index 7e68d20899..436ab3a8a8 100644
--- a/src/clock.c
+++ b/src/clock.c
@@ -49,8 +49,8 @@ void rt_system_tick_init(void)
  */
 rt_tick_t rt_tick_get(void)
 {
-	/* return the global tick */
-	return rt_tick;
+    /* return the global tick */
+    return rt_tick;
 }
 RTM_EXPORT(rt_tick_get);
 
@@ -59,11 +59,11 @@ RTM_EXPORT(rt_tick_get);
  */
 void rt_tick_set(rt_tick_t tick)
 {
-	rt_base_t level;
+    rt_base_t level;
 
-	level = rt_hw_interrupt_disable();
-	rt_tick = tick;
-	rt_hw_interrupt_enable(level);
+    level = rt_hw_interrupt_disable();
+    rt_tick = tick;
+    rt_hw_interrupt_enable(level);
 }
 
 /**
@@ -72,26 +72,26 @@ void rt_tick_set(rt_tick_t tick)
  */
 void rt_tick_increase(void)
 {
-	struct rt_thread *thread;
+    struct rt_thread *thread;
 
-	/* increase the global tick */
-	++ rt_tick;
+    /* increase the global tick */
+    ++ rt_tick;
 
-	/* check time slice */
-	thread = rt_thread_self();
+    /* check time slice */
+    thread = rt_thread_self();
 
-	-- thread->remaining_tick;
-	if (thread->remaining_tick == 0)
-	{
-		/* change to initialized tick */
-		thread->remaining_tick = thread->init_tick;
+    -- thread->remaining_tick;
+    if (thread->remaining_tick == 0)
+    {
+        /* change to initialized tick */
+        thread->remaining_tick = thread->init_tick;
 
-		/* yield */
-		rt_thread_yield();
-	}
+        /* yield */
+        rt_thread_yield();
+    }
 
-	/* check timer */
-	rt_timer_check();
+    /* check timer */
+    rt_timer_check();
 }
 
 /**
@@ -103,8 +103,8 @@ void rt_tick_increase(void)
  */
 rt_tick_t rt_tick_from_millisecond(rt_uint32_t ms)
 {
-	/* return the calculated tick */
-	return (RT_TICK_PER_SECOND * ms + 999) / 1000;
+    /* return the calculated tick */
+    return (RT_TICK_PER_SECOND * ms + 999) / 1000;
 }
 RTM_EXPORT(rt_tick_from_millisecond);