diff --git a/libc/include/wchar.h b/libc/include/wchar.h
index ee75148..e7c294f 100644
--- a/libc/include/wchar.h
+++ b/libc/include/wchar.h
@@ -136,8 +136,9 @@
 unsigned long long wcstoull_l(const wchar_t*, wchar_t**, int, locale_t) __INTRODUCED_IN(21);
 long double wcstold_l(const wchar_t*, wchar_t**, locale_t) __INTRODUCED_IN(21);
 
-int wcscoll_l(const wchar_t*, const wchar_t*, locale_t) __INTRODUCED_IN(21);
-size_t wcsxfrm_l(wchar_t*, const wchar_t*, size_t, locale_t) __INTRODUCED_IN(21);
+int wcscoll_l(const wchar_t* _Nonnull, const wchar_t* _Nonnull, locale_t) __purefunc
+    __INTRODUCED_IN(21);
+size_t wcsxfrm_l(wchar_t*, const wchar_t* _Nonnull, size_t, locale_t) __INTRODUCED_IN(21);
 
 size_t wcslcat(wchar_t*, const wchar_t*, size_t);
 size_t wcslcpy(wchar_t*, const wchar_t*, size_t);