diff --git a/include/rtdef.h b/include/rtdef.h
index 7e7e63594f3bedfff6afde0d99212bc17925afb0..f8d90ceadb8c4a9e5558f115e49b9735064d686f 100644
--- a/include/rtdef.h
+++ b/include/rtdef.h
@@ -496,6 +496,10 @@ typedef siginfo_t rt_siginfo_t;
 #define RT_THREAD_CTRL_CHANGE_PRIORITY  0x02                /**< Change thread priority. */
 #define RT_THREAD_CTRL_INFO             0x03                /**< Get thread information. */
 
+#ifdef RT_USING_LWP
+struct rt_lwp;
+#endif
+
 /**
  * Thread structure
  */