diff --git a/libc/include/bits/wchar_limits.h b/libc/include/bits/wchar_limits.h
index f779c1a..ffad604 100644
--- a/libc/include/bits/wchar_limits.h
+++ b/libc/include/bits/wchar_limits.h
@@ -29,6 +29,8 @@
 #ifndef _BITS_WCHAR_LIMITS_H_
 #define _BITS_WCHAR_LIMITS_H_
 
+#include <sys/cdefs.h>
+
 /* Both GCC and clang define __WCHAR_MAX__. */
 #define WCHAR_MAX __WCHAR_MAX__