diff --git a/libc/include/semaphore.h b/libc/include/semaphore.h
index 01d685b..5d66f7e 100644
--- a/libc/include/semaphore.h
+++ b/libc/include/semaphore.h
@@ -30,6 +30,7 @@
 #define _SEMAPHORE_H
 
 #include <sys/cdefs.h>
+#include <sys/types.h>
 
 __BEGIN_DECLS
 
@@ -44,16 +45,19 @@
 
 #define SEM_FAILED __BIONIC_CAST(reinterpret_cast, sem_t*, 0)
 
+int sem_clockwait(sem_t* __sem, clockid_t __clock, const struct timespec* __ts) __INTRODUCED_IN(30);
 int sem_destroy(sem_t* __sem);
 int sem_getvalue(sem_t* __sem, int* __value);
 int sem_init(sem_t* __sem, int __shared, unsigned int __value);
 int sem_post(sem_t* __sem);
 int sem_timedwait(sem_t* __sem, const struct timespec* __ts);
 /*
- * POSIX only supports using sem_timedwait() with CLOCK_REALTIME, however that is typically
- * inappropriate, since that clock can change dramatically, causing the timeout to either
+ * POSIX historically only supported using sem_timedwait() with CLOCK_REALTIME, however that is
+ * typically inappropriate, since that clock can change dramatically, causing the timeout to either
  * expire earlier or much later than intended.  This function is added to use a timespec based
  * on CLOCK_MONOTONIC that does not suffer from this issue.
+ * Note that sem_clockwait() allows specifying an arbitrary clock and has superseded this
+ * function.
  */
 int sem_timedwait_monotonic_np(sem_t* __sem, const struct timespec* __ts) __INTRODUCED_IN(28);
 int sem_trywait(sem_t* __sem);