diff --git a/libc/include/dlfcn.h b/libc/include/dlfcn.h
index 25a302f..5dc8350 100644
--- a/libc/include/dlfcn.h
+++ b/libc/include/dlfcn.h
@@ -46,8 +46,8 @@
 extern void* dlopen(const char*  filename, int flag);
 extern int dlclose(void*  handle);
 extern const char* dlerror(void);
-extern void* dlsym(void* handle, const char* symbol) __nonnull((2));
-extern void* dlvsym(void* handle, const char* symbol, const char* version) __nonnull((2, 3))
+extern void* dlsym(void* handle, const char* _Nonnull symbol);
+extern void* dlvsym(void* handle, const char* _Nonnull symbol, const char* _Nonnull version)
   __INTRODUCED_IN(24);
 extern int dladdr(const void* addr, Dl_info *info);
 
@@ -80,5 +80,3 @@
 __END_DECLS
 
 #endif /* __DLFCN_H */
-
-
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index 2df9b74..fd8aa00 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -135,49 +135,51 @@
 
 int pthread_atfork(void (*)(void), void (*)(void), void (*)(void)) __INTRODUCED_IN(21);
 
-int pthread_attr_destroy(pthread_attr_t*) __nonnull((1));
-int pthread_attr_getdetachstate(const pthread_attr_t*, int*) __nonnull((1, 2));
-int pthread_attr_getguardsize(const pthread_attr_t*, size_t*) __nonnull((1, 2));
-int pthread_attr_getschedparam(const pthread_attr_t*, struct sched_param*) __nonnull((1, 2));
-int pthread_attr_getschedpolicy(const pthread_attr_t*, int*) __nonnull((1, 2));
-int pthread_attr_getscope(const pthread_attr_t*, int*) __nonnull((1, 2));
-int pthread_attr_getstack(const pthread_attr_t*, void**, size_t*) __nonnull((1, 2, 3));
-int pthread_attr_getstacksize(const pthread_attr_t*, size_t*) __nonnull((1, 2));
-int pthread_attr_init(pthread_attr_t*) __nonnull((1));
-int pthread_attr_setdetachstate(pthread_attr_t*, int) __nonnull((1));
-int pthread_attr_setguardsize(pthread_attr_t*, size_t) __nonnull((1));
-int pthread_attr_setschedparam(pthread_attr_t*, const struct sched_param*) __nonnull((1, 2));
-int pthread_attr_setschedpolicy(pthread_attr_t*, int) __nonnull((1));
-int pthread_attr_setscope(pthread_attr_t*, int) __nonnull((1));
-int pthread_attr_setstack(pthread_attr_t*, void*, size_t) __nonnull((1));
-int pthread_attr_setstacksize(pthread_attr_t*, size_t) __nonnull((1));
+int pthread_attr_destroy(pthread_attr_t* _Nonnull);
+int pthread_attr_getdetachstate(const pthread_attr_t* _Nonnull, int* _Nonnull);
+int pthread_attr_getguardsize(const pthread_attr_t* _Nonnull, size_t* _Nonnull);
+int pthread_attr_getschedparam(const pthread_attr_t* _Nonnull, struct sched_param* _Nonnull);
+int pthread_attr_getschedpolicy(const pthread_attr_t* _Nonnull, int* _Nonnull);
+int pthread_attr_getscope(const pthread_attr_t* _Nonnull, int* _Nonnull);
+int pthread_attr_getstack(const pthread_attr_t* _Nonnull, void** _Nonnull, size_t* _Nonnull);
+int pthread_attr_getstacksize(const pthread_attr_t* _Nonnull, size_t* _Nonnull);
+int pthread_attr_init(pthread_attr_t* _Nonnull);
+int pthread_attr_setdetachstate(pthread_attr_t* _Nonnull, int);
+int pthread_attr_setguardsize(pthread_attr_t* _Nonnull, size_t);
+int pthread_attr_setschedparam(pthread_attr_t* _Nonnull, const struct sched_param* _Nonnull);
+int pthread_attr_setschedpolicy(pthread_attr_t* _Nonnull, int);
+int pthread_attr_setscope(pthread_attr_t* _Nonnull, int);
+int pthread_attr_setstack(pthread_attr_t* _Nonnull, void*, size_t);
+int pthread_attr_setstacksize(pthread_attr_t* _Nonnull, size_t);
 
-int pthread_condattr_destroy(pthread_condattr_t*) __nonnull((1));
-int pthread_condattr_getclock(const pthread_condattr_t*, clockid_t*) __nonnull((1, 2))
+int pthread_condattr_destroy(pthread_condattr_t* _Nonnull);
+int pthread_condattr_getclock(const pthread_condattr_t* _Nonnull, clockid_t* _Nonnull)
   __INTRODUCED_IN(21);
-int pthread_condattr_getpshared(const pthread_condattr_t*, int*) __nonnull((1, 2));
-int pthread_condattr_init(pthread_condattr_t*) __nonnull((1));
-int pthread_condattr_setclock(pthread_condattr_t*, clockid_t) __nonnull((1)) __INTRODUCED_IN(21);
-int pthread_condattr_setpshared(pthread_condattr_t*, int) __nonnull((1));
+int pthread_condattr_getpshared(const pthread_condattr_t* _Nonnull, int* _Nonnull);
+int pthread_condattr_init(pthread_condattr_t* _Nonnull);
+int pthread_condattr_setclock(pthread_condattr_t* _Nonnull, clockid_t) __INTRODUCED_IN(21);
+int pthread_condattr_setpshared(pthread_condattr_t* _Nonnull, int);
 
-int pthread_cond_broadcast(pthread_cond_t*) __nonnull((1));
-int pthread_cond_destroy(pthread_cond_t*) __nonnull((1));
-int pthread_cond_init(pthread_cond_t*, const pthread_condattr_t*) __nonnull((1));
-int pthread_cond_signal(pthread_cond_t*) __nonnull((1));
-int pthread_cond_timedwait(pthread_cond_t*, pthread_mutex_t*, const struct timespec*) __nonnull((1, 2, 3));
-int pthread_cond_wait(pthread_cond_t*, pthread_mutex_t*) __nonnull((1, 2));
+int pthread_cond_broadcast(pthread_cond_t* _Nonnull);
+int pthread_cond_destroy(pthread_cond_t* _Nonnull);
+int pthread_cond_init(pthread_cond_t* _Nonnull, const pthread_condattr_t*);
+int pthread_cond_signal(pthread_cond_t* _Nonnull);
+int pthread_cond_timedwait(pthread_cond_t* _Nonnull, pthread_mutex_t* _Nonnull,
+                           const struct timespec* _Nonnull);
+int pthread_cond_wait(pthread_cond_t* _Nonnull, pthread_mutex_t* _Nonnull);
 
-int pthread_create(pthread_t*, pthread_attr_t const*, void *(*)(void*), void*) __nonnull((1, 3));
+int pthread_create(pthread_t* _Nonnull, pthread_attr_t const*,
+                   void* (* _Nonnull start_routine)(void*), void*);
 int pthread_detach(pthread_t);
 void pthread_exit(void*) __noreturn;
 
 int pthread_equal(pthread_t, pthread_t);
 
-int pthread_getattr_np(pthread_t, pthread_attr_t*) __nonnull((2));
+int pthread_getattr_np(pthread_t, pthread_attr_t* _Nonnull);
 
-int pthread_getcpuclockid(pthread_t, clockid_t*) __nonnull((2));
+int pthread_getcpuclockid(pthread_t, clockid_t* _Nonnull);
 
-int pthread_getschedparam(pthread_t, int*, struct sched_param*) __nonnull((2, 3));
+int pthread_getschedparam(pthread_t, int* _Nonnull, struct sched_param* _Nonnull);
 
 void* pthread_getspecific(pthread_key_t);
 
@@ -185,79 +187,71 @@
 
 int pthread_join(pthread_t, void**);
 
-int pthread_key_create(pthread_key_t*, void (*)(void*)) __nonnull((1));
+int pthread_key_create(pthread_key_t* _Nonnull, void (*)(void*));
 int pthread_key_delete(pthread_key_t);
 
-int pthread_mutexattr_destroy(pthread_mutexattr_t*) __nonnull((1));
-int pthread_mutexattr_getpshared(const pthread_mutexattr_t*, int*) __nonnull((1, 2));
-int pthread_mutexattr_gettype(const pthread_mutexattr_t*, int*) __nonnull((1, 2));
-int pthread_mutexattr_init(pthread_mutexattr_t*) __nonnull((1));
-int pthread_mutexattr_setpshared(pthread_mutexattr_t*, int) __nonnull((1));
-int pthread_mutexattr_settype(pthread_mutexattr_t*, int) __nonnull((1));
+int pthread_mutexattr_destroy(pthread_mutexattr_t* _Nonnull);
+int pthread_mutexattr_getpshared(const pthread_mutexattr_t* _Nonnull, int* _Nonnull);
+int pthread_mutexattr_gettype(const pthread_mutexattr_t* _Nonnull, int* _Nonnull);
+int pthread_mutexattr_init(pthread_mutexattr_t* _Nonnull);
+int pthread_mutexattr_setpshared(pthread_mutexattr_t* _Nonnull, int);
+int pthread_mutexattr_settype(pthread_mutexattr_t* _Nonnull, int);
 
-int pthread_mutex_destroy(pthread_mutex_t*) __nonnull((1));
-int pthread_mutex_init(pthread_mutex_t*, const pthread_mutexattr_t*) __nonnull((1));
-#if !defined(__LP64__)
-int pthread_mutex_lock(pthread_mutex_t*) /* __nonnull((1)) */;
-#else
-int pthread_mutex_lock(pthread_mutex_t*) __nonnull((1));
-#endif
-int pthread_mutex_timedlock(pthread_mutex_t*, const struct timespec*) __nonnull((1, 2))
+int pthread_mutex_destroy(pthread_mutex_t* _Nonnull);
+int pthread_mutex_init(pthread_mutex_t* _Nonnull, const pthread_mutexattr_t*);
+int pthread_mutex_lock(pthread_mutex_t* _Nonnull);
+int pthread_mutex_timedlock(pthread_mutex_t* _Nonnull, const struct timespec* _Nonnull)
   __INTRODUCED_IN(21);
-int pthread_mutex_trylock(pthread_mutex_t*) __nonnull((1));
-#if !defined(__LP4__)
-int pthread_mutex_unlock(pthread_mutex_t*) /* __nonnull((1)) */;
-#else
-int pthread_mutex_unlock(pthread_mutex_t*) __nonnull((1));
-#endif
+int pthread_mutex_trylock(pthread_mutex_t* _Nonnull);
+int pthread_mutex_unlock(pthread_mutex_t* _Nonnull);
 
-int pthread_once(pthread_once_t*, void (*)(void)) __nonnull((1, 2));
+int pthread_once(pthread_once_t* _Nonnull, void (* _Nonnull init_routine)(void));
 
-int pthread_rwlockattr_init(pthread_rwlockattr_t*) __nonnull((1));
-int pthread_rwlockattr_destroy(pthread_rwlockattr_t*) __nonnull((1));
-int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t*, int*) __nonnull((1, 2));
-int pthread_rwlockattr_setpshared(pthread_rwlockattr_t*, int) __nonnull((1));
-int pthread_rwlockattr_getkind_np(const pthread_rwlockattr_t*, int*) __nonnull((1, 2))
+int pthread_rwlockattr_init(pthread_rwlockattr_t* _Nonnull);
+int pthread_rwlockattr_destroy(pthread_rwlockattr_t* _Nonnull);
+int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t* _Nonnull, int* _Nonnull);
+int pthread_rwlockattr_setpshared(pthread_rwlockattr_t* _Nonnull, int);
+int pthread_rwlockattr_getkind_np(const pthread_rwlockattr_t* _Nonnull, int* _Nonnull)
   __INTRODUCED_IN(23);
-int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t*, int) __nonnull((1)) __INTRODUCED_IN(23);
+int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t* _Nonnull, int) __INTRODUCED_IN(23);
 
-int pthread_rwlock_destroy(pthread_rwlock_t*) __nonnull((1));
-int pthread_rwlock_init(pthread_rwlock_t*, const pthread_rwlockattr_t*) __nonnull((1));
-int pthread_rwlock_rdlock(pthread_rwlock_t*) __nonnull((1));
-int pthread_rwlock_timedrdlock(pthread_rwlock_t*, const struct timespec*) __nonnull((1, 2));
-int pthread_rwlock_timedwrlock(pthread_rwlock_t*, const struct timespec*) __nonnull((1, 2));
-int pthread_rwlock_tryrdlock(pthread_rwlock_t*) __nonnull((1));
-int pthread_rwlock_trywrlock(pthread_rwlock_t*) __nonnull((1));
-int pthread_rwlock_unlock(pthread_rwlock_t *) __nonnull((1));
-int pthread_rwlock_wrlock(pthread_rwlock_t*) __nonnull((1));
+int pthread_rwlock_destroy(pthread_rwlock_t* _Nonnull);
+int pthread_rwlock_init(pthread_rwlock_t* _Nonnull, const pthread_rwlockattr_t*);
+int pthread_rwlock_rdlock(pthread_rwlock_t* _Nonnull);
+int pthread_rwlock_timedrdlock(pthread_rwlock_t* _Nonnull, const struct timespec* _Nonnull);
+int pthread_rwlock_timedwrlock(pthread_rwlock_t* _Nonnull, const struct timespec* _Nonnull);
+int pthread_rwlock_tryrdlock(pthread_rwlock_t* _Nonnull);
+int pthread_rwlock_trywrlock(pthread_rwlock_t* _Nonnull);
+int pthread_rwlock_unlock(pthread_rwlock_t* _Nonnull);
+int pthread_rwlock_wrlock(pthread_rwlock_t* _Nonnull);
 
-int pthread_barrierattr_init(pthread_barrierattr_t* attr) __nonnull((1)) __INTRODUCED_IN(24);
-int pthread_barrierattr_destroy(pthread_barrierattr_t* attr) __nonnull((1)) __INTRODUCED_IN(24);
-int pthread_barrierattr_getpshared(pthread_barrierattr_t* attr, int* pshared) __nonnull((1, 2))
+int pthread_barrierattr_init(pthread_barrierattr_t* _Nonnull attr) __INTRODUCED_IN(24);
+int pthread_barrierattr_destroy(pthread_barrierattr_t* _Nonnull attr) __INTRODUCED_IN(24);
+int pthread_barrierattr_getpshared(pthread_barrierattr_t* _Nonnull attr, int* _Nonnull pshared)
   __INTRODUCED_IN(24);
-int pthread_barrierattr_setpshared(pthread_barrierattr_t* attr, int pshared) __nonnull((1))
+int pthread_barrierattr_setpshared(pthread_barrierattr_t* _Nonnull attr, int pshared)
   __INTRODUCED_IN(24);
 
-int pthread_barrier_init(pthread_barrier_t*, const pthread_barrierattr_t*, unsigned) __nonnull((1))
+int pthread_barrier_init(pthread_barrier_t* _Nonnull, const pthread_barrierattr_t*, unsigned)
   __INTRODUCED_IN(24);
-int pthread_barrier_destroy(pthread_barrier_t*) __nonnull((1)) __INTRODUCED_IN(24);
-int pthread_barrier_wait(pthread_barrier_t*) __nonnull((1)) __INTRODUCED_IN(24);
+int pthread_barrier_destroy(pthread_barrier_t* _Nonnull) __INTRODUCED_IN(24);
+int pthread_barrier_wait(pthread_barrier_t* _Nonnull) __INTRODUCED_IN(24);
 
-int pthread_spin_destroy(pthread_spinlock_t*) __nonnull((1)) __INTRODUCED_IN(24);
-int pthread_spin_init(pthread_spinlock_t*, int) __nonnull((1)) __INTRODUCED_IN(24);
-int pthread_spin_lock(pthread_spinlock_t*) __nonnull((1)) __INTRODUCED_IN(24);
-int pthread_spin_trylock(pthread_spinlock_t*) __nonnull((1)) __INTRODUCED_IN(24);
-int pthread_spin_unlock(pthread_spinlock_t*) __nonnull((1)) __INTRODUCED_IN(24);
+int pthread_spin_destroy(pthread_spinlock_t* _Nonnull) __INTRODUCED_IN(24);
+int pthread_spin_init(pthread_spinlock_t* _Nonnull, int) __INTRODUCED_IN(24);
+int pthread_spin_lock(pthread_spinlock_t* _Nonnull) __INTRODUCED_IN(24);
+int pthread_spin_trylock(pthread_spinlock_t* _Nonnull) __INTRODUCED_IN(24);
+int pthread_spin_unlock(pthread_spinlock_t* _Nonnull) __INTRODUCED_IN(24);
 
 pthread_t pthread_self(void) __pure2;
 
 #if defined(__USE_GNU)
-int pthread_getname_np(pthread_t, char*, size_t) __nonnull((2)) __INTRODUCED_IN_FUTURE;
+int pthread_getname_np(pthread_t, char* _Nonnull, size_t) __INTRODUCED_IN_FUTURE;
 #endif
 /* TODO: this should be __USE_GNU too. */
-int pthread_setname_np(pthread_t, const char*) __nonnull((2));
+int pthread_setname_np(pthread_t, const char* _Nonnull);
 
-int pthread_setschedparam(pthread_t, int, const struct sched_param*) __nonnull((3));
+int pthread_setschedparam(pthread_t, int, const struct sched_param* _Nonnull);
 
 int pthread_setspecific(pthread_key_t, const void*);
 
diff --git a/libc/include/signal.h b/libc/include/signal.h
index 4b5e4ac..d9f43de 100644
--- a/libc/include/signal.h
+++ b/libc/include/signal.h
@@ -120,10 +120,10 @@
 __BIONIC_LEGACY_INLINE int sigfillset(sigset_t*);
 __BIONIC_LEGACY_INLINE int sigismember(const sigset_t*, int);
 
-extern int sigpending(sigset_t*) __nonnull((1));
+extern int sigpending(sigset_t* _Nonnull);
 extern int sigprocmask(int, const sigset_t*, sigset_t*);
-extern int sigsuspend(const sigset_t*) __nonnull((1));
-extern int sigwait(const sigset_t*, int*) __nonnull((1, 2));
+extern int sigsuspend(const sigset_t* _Nonnull);
+extern int sigwait(const sigset_t* _Nonnull, int* _Nonnull);
 
 extern int sighold(int)
   __attribute__((deprecated("use sigprocmask() or pthread_sigmask() instead")))
diff --git a/libc/include/string.h b/libc/include/string.h
index 3f98af1..f39a86b 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -120,10 +120,10 @@
  */
 
 #if defined(__cplusplus)
-extern "C++" char* basename(char*) __RENAME(__gnu_basename) __nonnull((1));
-extern "C++" const char* basename(const char*) __RENAME(__gnu_basename) __nonnull((1));
+extern "C++" char* basename(char* _Nonnull) __RENAME(__gnu_basename);
+extern "C++" const char* basename(const char* _Nonnull) __RENAME(__gnu_basename);
 #else
-extern char* basename(const char*) __RENAME(__gnu_basename) __nonnull((1)) __INTRODUCED_IN(23);
+extern char* basename(const char* _Nonnull) __RENAME(__gnu_basename) __INTRODUCED_IN(23);
 #endif
 #endif
 
diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 3fcf163..7b06967 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -159,6 +159,38 @@
 
 #define __nonnull(args) __attribute__((__nonnull__ args))
 
+/*
+ * _Nonnull is similar to the nonnull attribute in that it will instruct
+ * compilers to warn the user if it can prove that a null argument is being
+ * passed. Unlike the nonnull attribute, this annotation indicated that a value
+ * *should not* be null, not that it *cannot* be null, or even that the behavior
+ * is undefined. The important distinction is that the optimizer will perform
+ * surprising optimizations like the following:
+ *
+ *     void foo(void*) __attribute__(nonnull, 1);
+ *
+ *     int bar(int* p) {
+ *       foo(p);
+ *
+ *       // The following null check will be elided because nonnull attribute
+ *       // means that, since we call foo with p, p can be assumed to not be
+ *       // null. Thus this will crash if we are called with a null pointer.
+ *       if (src != NULL) {
+ *         return *p;
+ *       }
+ *       return 0;
+ *     }
+ *
+ *     int main() {
+ *       return bar(NULL);
+ *     }
+ *
+ * http://clang.llvm.org/docs/AttributeReference.html#nonnull
+ */
+#if !(defined(__clang__) && __has_feature(nullability))
+#define _Nonnull
+#endif
+
 #define __printflike(x, y) __attribute__((__format__(printf, x, y))) __nonnull((x))
 #define __scanflike(x, y) __attribute__((__format__(scanf, x, y))) __nonnull((x))
 
diff --git a/libc/include/sys/signalfd.h b/libc/include/sys/signalfd.h
index 5b67822..084a528 100644
--- a/libc/include/sys/signalfd.h
+++ b/libc/include/sys/signalfd.h
@@ -35,7 +35,7 @@
 
 __BEGIN_DECLS
 
-extern int signalfd(int fd, const sigset_t* mask, int flags) __nonnull((2)) __INTRODUCED_IN(21);
+extern int signalfd(int fd, const sigset_t* _Nonnull mask, int flags) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/statvfs.h b/libc/include/sys/statvfs.h
index e12f069..1f00b9d 100644
--- a/libc/include/sys/statvfs.h
+++ b/libc/include/sys/statvfs.h
@@ -59,12 +59,12 @@
 #define ST_NODIRATIME  0x0800
 #define ST_RELATIME    0x1000
 
-extern int statvfs(const char* __restrict, struct statvfs* __restrict) __nonnull((1, 2))
+extern int statvfs(const char* __restrict _Nonnull, struct statvfs* __restrict _Nonnull)
   __INTRODUCED_IN(21);
-extern int statvfs64(const char* __restrict, struct statvfs64* __restrict) __nonnull((1, 2))
+extern int statvfs64(const char* __restrict _Nonnull, struct statvfs64* __restrict _Nonnull)
   __INTRODUCED_IN(21);
-extern int fstatvfs(int, struct statvfs*) __nonnull((2)) __INTRODUCED_IN(21);
-extern int fstatvfs64(int, struct statvfs64*) __nonnull((2)) __INTRODUCED_IN(21);
+extern int fstatvfs(int, struct statvfs* _Nonnull) __INTRODUCED_IN(21);
+extern int fstatvfs64(int, struct statvfs64* _Nonnull) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/swap.h b/libc/include/sys/swap.h
index b1f9295..fe14a30 100644
--- a/libc/include/sys/swap.h
+++ b/libc/include/sys/swap.h
@@ -38,8 +38,8 @@
 #define SWAP_FLAG_PRIO_MASK 0x7fff
 #define SWAP_FLAG_PRIO_SHIFT 0
 
-extern int swapon(const char*, int) __nonnull((1)) __INTRODUCED_IN(21);
-extern int swapoff(const char*) __nonnull((1)) __INTRODUCED_IN(21);
+extern int swapon(const char* _Nonnull, int) __INTRODUCED_IN(21);
+extern int swapoff(const char* _Nonnull) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/vfs.h b/libc/include/sys/vfs.h
index 9f04b28..bf094dc 100644
--- a/libc/include/sys/vfs.h
+++ b/libc/include/sys/vfs.h
@@ -137,10 +137,10 @@
 #define XENIX_SUPER_MAGIC     0x012FF7B4
 #define XFS_SUPER_MAGIC       0x58465342
 
-extern int statfs(const char*, struct statfs*) __nonnull((1, 2));
-extern int statfs64(const char*, struct statfs64*) __nonnull((1, 2)) __INTRODUCED_IN(21);
-extern int fstatfs(int, struct statfs*) __nonnull((2));
-extern int fstatfs64(int, struct statfs64*) __nonnull((2)) __INTRODUCED_IN(21);
+extern int statfs(const char* _Nonnull, struct statfs* _Nonnull);
+extern int statfs64(const char* _Nonnull, struct statfs64* _Nonnull) __INTRODUCED_IN(21);
+extern int fstatfs(int, struct statfs* _Nonnull);
+extern int fstatfs64(int, struct statfs64* _Nonnull) __INTRODUCED_IN(21);
 
 __END_DECLS