diff --git a/include/rtdef.h b/include/rtdef.h
index edfbbd854..992a1b855 100644
--- a/include/rtdef.h
+++ b/include/rtdef.h
@@ -596,7 +596,7 @@ struct rt_memheap
     struct rt_memheap_item *free_list;                  /**< free block list */
     struct rt_memheap_item  free_header;                /**< free block list header */
 
-	struct rt_mutex         lock;                       /**< mutex lock */
+    struct rt_mutex         lock;                       /**< mutex lock */
 };
 
 /**