diff --git a/include/stdio.h b/include/stdio.h
index b0190d25eb4f..ee3ab3bfb986 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -48,10 +48,13 @@ typedef	__size_t	size_t;
 #define	_SIZE_T_DECLARED
 #endif
 
+#if __EXT1_VISIBLE
+/* ISO/IEC 9899:2011 K.3.3.2 */
 #ifndef _RSIZE_T_DEFINED
 #define _RSIZE_T_DEFINED
 typedef size_t rsize_t;
 #endif
+#endif /* __EXT1_VISIBLE */
 
 #if __POSIX_VISIBLE >= 200809
 #ifndef _OFF_T_DECLARED