diff --git a/libc/include/time.h b/libc/include/time.h
index 0db14ff..4b005c6 100644
--- a/libc/include/time.h
+++ b/libc/include/time.h
@@ -37,7 +37,7 @@
 
 #define CLOCKS_PER_SEC 1000000
 
-extern char* tzname[];
+extern char* _Nonnull tzname[];
 extern int daylight;
 extern long int timezone;
 
@@ -54,62 +54,64 @@
   int tm_yday;
   int tm_isdst;
   long int tm_gmtoff;
-  const char* tm_zone;
+  const char* _Nullable tm_zone;
 };
 
 #define TM_ZONE tm_zone
 
-time_t time(time_t* __t);
-int nanosleep(const struct timespec* __request, struct timespec* __remainder);
+time_t time(time_t* _Nullable __t);
+int nanosleep(const struct timespec* _Nonnull __request, struct timespec* _Nullable __remainder);
 
-char* asctime(const struct tm* __tm);
-char* asctime_r(const struct tm* __tm, char* __buf);
+char* _Nullable asctime(const struct tm* _Nonnull __tm);
+char* _Nullable asctime_r(const struct tm* _Nonnull __tm, char* _Nonnull __buf);
 
 double difftime(time_t __lhs, time_t __rhs);
-time_t mktime(struct tm* __tm);
+time_t mktime(struct tm* _Nonnull __tm);
 
-struct tm* localtime(const time_t* __t);
-struct tm* localtime_r(const time_t* __t, struct tm* __tm);
+struct tm* _Nullable localtime(const time_t* _Nonnull __t);
+struct tm* _Nullable localtime_r(const time_t* _Nonnull __t, struct tm* _Nonnull __tm);
 
-struct tm* gmtime(const time_t* __t);
-struct tm* gmtime_r(const time_t* __t, struct tm* __tm);
+struct tm* _Nullable gmtime(const time_t* _Nonnull __t);
+struct tm* _Nullable gmtime_r(const time_t* _Nonnull __t, struct tm* _Nonnull __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);
+char* _Nullable strptime(const char* _Nonnull __s, const char* _Nonnull __fmt, struct tm* _Nonnull __tm) __strftimelike(2);
+char* _Nullable strptime_l(const char* _Nonnull __s, const char* _Nonnull __fmt, struct tm* _Nonnull __tm, locale_t _Nonnull __l) __strftimelike(2) __INTRODUCED_IN(28);
 
-size_t strftime(char* __buf, size_t __n, const char* __fmt, const struct tm* __tm) __strftimelike(3);
+size_t strftime(char* _Nonnull __buf, size_t __n, const char* _Nonnull __fmt, const struct tm* _Nullable __tm) __strftimelike(3);
 #if __ANDROID_API__ >= 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);
+size_t strftime_l(char* _Nonnull __buf, size_t __n, const char* _Nonnull __fmt, const struct tm* _Nullable __tm, locale_t _Nonnull __l) __strftimelike(3) __INTRODUCED_IN(21);
 #else
 // Implemented as static inline before 21.
 #endif
 
-char* ctime(const time_t* __t);
-char* ctime_r(const time_t* __t, char* __buf);
+
+char* _Nullable ctime(const time_t* _Nonnull __t);
+char* _Nullable ctime_r(const time_t* _Nonnull __t, char* _Nonnull __buf);
 
 void tzset(void);
 
 clock_t clock(void);
 
-int clock_getcpuclockid(pid_t __pid, clockid_t* __clock) __INTRODUCED_IN(23);
+int clock_getcpuclockid(pid_t __pid, clockid_t* _Nonnull __clock) __INTRODUCED_IN(23);
 
-int clock_getres(clockid_t __clock, struct timespec* __resolution);
-int clock_gettime(clockid_t __clock, struct timespec* __ts);
-int clock_nanosleep(clockid_t __clock, int __flags, const struct timespec* __request, struct timespec* __remainder);
-int clock_settime(clockid_t __clock, const struct timespec* __ts);
 
-int timer_create(clockid_t __clock, struct sigevent* __event, timer_t* __timer_ptr);
-int timer_delete(timer_t __timer);
-int timer_settime(timer_t __timer, int __flags, const struct itimerspec* __new_value, struct itimerspec* __old_value);
-int timer_gettime(timer_t __timer, struct itimerspec* __ts);
-int timer_getoverrun(timer_t __timer);
+int clock_getres(clockid_t __clock, struct timespec* _Nullable __resolution);
+int clock_gettime(clockid_t __clock, struct timespec* _Nonnull __ts);
+int clock_nanosleep(clockid_t __clock, int __flags, const struct timespec* _Nonnull __request, struct timespec* _Nullable __remainder);
+int clock_settime(clockid_t __clock, const struct timespec* _Nonnull __ts);
+
+int timer_create(clockid_t __clock, struct sigevent* _Nullable __event, timer_t _Nonnull * _Nonnull __timer_ptr);
+int timer_delete(timer_t _Nonnull __timer);
+int timer_settime(timer_t _Nonnull __timer, int __flags, const struct itimerspec* _Nonnull __new_value, struct itimerspec* _Nullable __old_value);
+int timer_gettime(timer_t _Nonnull _timer, struct itimerspec* _Nonnull __ts);
+int timer_getoverrun(timer_t _Nonnull __timer);
 
 /* Non-standard extensions that are in the BSDs and glibc. */
-time_t timelocal(struct tm* __tm);
-time_t timegm(struct tm* __tm);
+time_t timelocal(struct tm* _Nonnull __tm);
+time_t timegm(struct tm* _Nonnull __tm);
 
 #define TIME_UTC 1
-int timespec_get(struct timespec* __ts, int __base) __INTRODUCED_IN(29);
+int timespec_get(struct timespec* _Nonnull __ts, int __base) __INTRODUCED_IN(29);
 
 __END_DECLS