diff --git a/include/rtdef.h b/include/rtdef.h
index 9b12093dc7..8c7e6e8c43 100644
--- a/include/rtdef.h
+++ b/include/rtdef.h
@@ -655,7 +655,7 @@ struct rt_semaphore
 {
     struct rt_ipc_object parent;                        /**< inherit from ipc_object */
 
-    rt_uint16_t          value;                         /**< value of semaphore. */
+    rt_uint32_t          value;                         /**< value of semaphore. */
 };
 typedef struct rt_semaphore *rt_sem_t;
 #endif