diff --git a/include/rtdef.h b/include/rtdef.h
index edfbbd85458ea6b44c6ac478edc5f5f86cef1328..992a1b8555437d4fa769cdd610a8e1888081f328 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 */
 };
 
 /**