diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 26dd9a2..c270bb5 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -120,6 +120,7 @@
 
 #define __printflike(x, y) __attribute__((__format__(printf, x, y)))
 #define __scanflike(x, y) __attribute__((__format__(scanf, x, y)))
+#define __strftimelike(x) __attribute__((__format__(strftime, x, 0)))
 
 /*
  * GNU C version 2.96 added explicit branch prediction so that
diff --git a/libc/include/time.h b/libc/include/time.h
index 8e78949..17751d7 100644
--- a/libc/include/time.h
+++ b/libc/include/time.h
@@ -74,11 +74,12 @@
 struct tm* gmtime(const time_t* __t);
 struct tm* gmtime_r(const time_t* __t, struct tm* __tm);
 
-char* strptime(const char* __s, const char* __fmt, struct tm* __tm);
-size_t strftime(char* __buf, size_t __n, const char* __fmt, const struct tm* __tm);
+char* strptime(const char* __s, const char* __fmt, struct tm* __tm) __strftimelike(2);
+char* strptime_l(const char* __s, const char* __fmt, struct tm* __tm, locale_t __l) __strftimelike(2) __INTRODUCED_IN(28);
 
+size_t strftime(char* __buf, size_t __n, const char* __fmt, const struct tm* __tm) __strftimelike(3);
 #if __ANDROID_API__ >= __ANDROID_API_L__
-size_t strftime_l(char* __buf, size_t __n, const char* __fmt, const struct tm* __tm, locale_t __l) __INTRODUCED_IN(21);
+size_t strftime_l(char* __buf, size_t __n, const char* __fmt, const struct tm* __tm, locale_t __l) __strftimelike(3) __INTRODUCED_IN(21);
 #else
 // Implemented as static inline before 21.
 #endif
diff --git a/libc/include/wchar.h b/libc/include/wchar.h
index 1cf498c83..f33af5f 100644
--- a/libc/include/wchar.h
+++ b/libc/include/wchar.h
@@ -81,6 +81,7 @@
 wchar_t* wcscpy(wchar_t* __dst, const wchar_t* __src);
 size_t wcscspn(const wchar_t* __s, const wchar_t* __accept);
 size_t wcsftime(wchar_t* __buf, size_t __n, const wchar_t* __fmt, const struct tm* __tm);
+size_t wcsftime_l(wchar_t* __buf, size_t __n, const wchar_t* __fmt, const struct tm* __tm, locale_t __l) __INTRODUCED_IN(28);
 size_t wcslen(const wchar_t* __s);
 int wcsncasecmp(const wchar_t* __lhs, const wchar_t* __rhs, size_t __n);
 int wcsncasecmp_l(const wchar_t* __lhs, const wchar_t* __rhs, size_t __n, locale_t __l) __INTRODUCED_IN(23);
@@ -94,12 +95,16 @@
 size_t wcsspn(const wchar_t* __s, const wchar_t* __accept);
 wchar_t* wcsstr(const wchar_t* __haystack, const wchar_t* __needle);
 double wcstod(const wchar_t* __s, wchar_t** __end_ptr);
+double wcstod_l(const wchar_t* __s, wchar_t** __end_ptr, locale_t __l) __INTRODUCED_IN(28);
 float wcstof(const wchar_t* __s, wchar_t** __end_ptr) __INTRODUCED_IN(21);
+float wcstof_l(const wchar_t* __s, wchar_t** __end_ptr, locale_t __l) __INTRODUCED_IN(28);
 wchar_t* wcstok(wchar_t* __s, const wchar_t* __delimiter, wchar_t** __ptr);
 long wcstol(const wchar_t* __s, wchar_t** __end_ptr, int __base);
+long wcstol_l(const wchar_t* __s, wchar_t** __end_ptr, int __base, locale_t __l) __INTRODUCED_IN(28);
 long long wcstoll(const wchar_t* __s, wchar_t** __end_ptr, int __base) __INTRODUCED_IN(21);
 long double wcstold(const wchar_t* __s, wchar_t** __end_ptr) __RENAME_LDBL(wcstod, 3, 21);
 unsigned long wcstoul(const wchar_t* __s, wchar_t** __end_ptr, int __base);
+unsigned long wcstoul_l(const wchar_t* __s, wchar_t** __end_ptr, int __base, locale_t __l) __INTRODUCED_IN(28);
 unsigned long long wcstoull(const wchar_t* __s, wchar_t** __end_ptr, int __base) __INTRODUCED_IN(21);
 int wcswidth(const wchar_t* __s, size_t __n);
 size_t wcsxfrm(wchar_t* __dst, const wchar_t* __src, size_t __n);