diff --git a/libc/include/sys/select.h b/libc/include/sys/select.h
index 06914a6..8c6c2ff 100644
--- a/libc/include/sys/select.h
+++ b/libc/include/sys/select.h
@@ -71,9 +71,9 @@
     } \
   } while (0)
 
-void __FD_CLR_chk(int, fd_set*, size_t) __INTRODUCED_IN(21);
-void __FD_SET_chk(int, fd_set*, size_t) __INTRODUCED_IN(21);
-int __FD_ISSET_chk(int, const fd_set*, size_t) __INTRODUCED_IN(21);
+void __FD_CLR_chk(int, fd_set* _Nonnull , size_t) __INTRODUCED_IN(21);
+void __FD_SET_chk(int, fd_set* _Nonnull, size_t) __INTRODUCED_IN(21);
+int __FD_ISSET_chk(int, const fd_set* _Nonnull, size_t) __INTRODUCED_IN(21);
 
 #define __FD_CLR(fd, set) (__FDS_BITS(fd_set*,set)[__FDELT(fd)] &= ~__FDMASK(fd))
 #define __FD_SET(fd, set) (__FDS_BITS(fd_set*,set)[__FDELT(fd)] |= __FDMASK(fd))
@@ -95,7 +95,7 @@
  * Returns the number of ready file descriptors on success, 0 for timeout,
  * and returns -1 and sets `errno` on failure.
  */
-int select(int __max_fd_plus_one, fd_set* __read_fds, fd_set* __write_fds, fd_set* __exception_fds, struct timeval* __timeout);
+int select(int __max_fd_plus_one, fd_set* _Nullable __read_fds, fd_set* _Nullable __write_fds, fd_set* _Nullable __exception_fds, struct timeval* _Nullable __timeout);
 
 /**
  * [pselect(2)](http://man7.org/linux/man-pages/man2/select.2.html) waits on a
@@ -106,7 +106,7 @@
  * Returns the number of ready file descriptors on success, 0 for timeout,
  * and returns -1 and sets `errno` on failure.
  */
-int pselect(int __max_fd_plus_one, fd_set* __read_fds, fd_set* __write_fds, fd_set* __exception_fds, const struct timespec* __timeout, const sigset_t* __mask);
+int pselect(int __max_fd_plus_one, fd_set* _Nullable __read_fds, fd_set* _Nullable __write_fds, fd_set* _Nullable __exception_fds, const struct timespec* _Nullable __timeout, const sigset_t* _Nullable __mask);
 
 /**
  * [pselect64(2)](http://man7.org/linux/man-pages/man2/select.2.html) waits on a
@@ -119,6 +119,6 @@
  *
  * Available since API level 28.
  */
-int pselect64(int __max_fd_plus_one, fd_set* __read_fds, fd_set* __write_fds, fd_set* __exception_fds, const struct timespec* __timeout, const sigset64_t* __mask) __INTRODUCED_IN(28);
+int pselect64(int __max_fd_plus_one, fd_set* _Nullable __read_fds, fd_set* _Nullable __write_fds, fd_set* _Nullable __exception_fds, const struct timespec* _Nullable __timeout, const sigset64_t* _Nullable __mask) __INTRODUCED_IN(28);
 
 __END_DECLS