diff --git a/libc/include/ftw.h b/libc/include/ftw.h
index a289643..c5fa4de 100644
--- a/libc/include/ftw.h
+++ b/libc/include/ftw.h
@@ -55,10 +55,10 @@
 };
 
 __BEGIN_DECLS
-int ftw(const char* __dir_path, int (*__callback)(const char*, const struct stat*, int), int __max_fd_count) __INTRODUCED_IN(17);
-int nftw(const char* __dir_path, int (*__callback)(const char*, const struct stat*, int, struct FTW*), int __max_fd_count, int __flags) __INTRODUCED_IN(17);
-int ftw64(const char* __dir_path, int (*__callback)(const char*, const struct stat64*, int), int __max_fd_count) __RENAME_STAT64(ftw, 17, 21);
-int nftw64(const char* __dir_path, int (*__callback)(const char*, const struct stat64*, int, struct FTW*), int __max_fd_count, int __flags) __RENAME_STAT64(nftw, 17, 21);
+int ftw(const char* _Nonnull __dir_path, int (* _Nonnull __callback)(const char* _Nonnull, const struct stat* _Nonnull, int), int __max_fd_count) __INTRODUCED_IN(17);
+int nftw(const char* _Nonnull __dir_path, int (* _Nonnull __callback)(const char* _Nonnull, const struct stat* _Nonnull, int, struct FTW* _Nonnull), int __max_fd_count, int __flags) __INTRODUCED_IN(17);
+int ftw64(const char* _Nonnull __dir_path, int (* _Nonnull __callback)(const char* _Nonnull, const struct stat64* _Nonnull, int), int __max_fd_count) __RENAME_STAT64(ftw, 17, 21);
+int nftw64(const char* _Nonnull __dir_path, int (* _Nonnull __callback)(const char* _Nonnull, const struct stat64* _Nonnull, int, struct FTW* _Nonnull), int __max_fd_count, int __flags) __RENAME_STAT64(nftw, 17, 21);
 __END_DECLS
 
 #endif