diff --git a/conform/data/semaphore.h-data b/conform/data/semaphore.h-data
index 066c2f7..019aaa1 100644
--- a/conform/data/semaphore.h-data
+++ b/conform/data/semaphore.h-data
@@ -11,6 +11,7 @@ function {sem_t*} sem_open (const char*, int, ...)
 function int sem_post (sem_t*)
 # if !defined POSIX && !defined UNIX98
 function int sem_timedwait (sem_t*, const struct timespec*)
+function int sem_clockwait (sem_t*, clockid_t, const struct timespec*)
 # endif
 function int sem_trywait (sem_t*)
 function int sem_unlink (const char*)
diff --git a/manual/threads.texi b/manual/threads.texi
index 87fda7d..674267c 100644
--- a/manual/threads.texi
+++ b/manual/threads.texi
@@ -669,6 +669,16 @@ The system does not have sufficient memory.
 @end table
 @end deftypefun
 
+@comment semaphore.h
+@comment POSIX-proposed
+@deftypefun int sem_clockwait (sem_t *@var{sem}, clockid_t @var{clockid},
+                               const struct timespec *@var{abstime})
+Behaves like @code{sem_timedwait} except the time @var{abstime} is measured
+against the clock specified by @var{clockid} rather than
+@code{CLOCK_REALTIME}. Currently, @var{clockid} must be either
+@code{CLOCK_MONOTONIC} or @code{CLOCK_REALTIME}.
+@end deftypefun
+
 @c FIXME these are undocumented:
 @c pthread_atfork
 @c pthread_attr_destroy
diff --git a/nptl/Makefile b/nptl/Makefile
index 5acfdcc..4c9f5d3 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -114,7 +114,7 @@ libpthread-routines = nptl-init nptlfreeres vars events version pt-interp \
 		      sem_init sem_destroy \
 		      sem_open sem_close sem_unlink \
 		      sem_getvalue \
-		      sem_wait sem_timedwait sem_post \
+		      sem_wait sem_timedwait sem_clockwait sem_post \
 		      cleanup cleanup_defer cleanup_compat \
 		      cleanup_defer_compat unwind \
 		      pt-longjmp pt-cleanup\
@@ -194,6 +194,7 @@ CFLAGS-pthread_once.c += $(uses-callbacks) -fexceptions \
 CFLAGS-pthread_cond_wait.c += -fexceptions -fasynchronous-unwind-tables
 CFLAGS-sem_wait.c += -fexceptions -fasynchronous-unwind-tables
 CFLAGS-sem_timedwait.c += -fexceptions -fasynchronous-unwind-tables
+CFLAGS-sem_clockwait.c = -fexceptions -fasynchronous-unwind-tables
 
 # These are the function wrappers we have to duplicate here.
 CFLAGS-fcntl.c += -fexceptions -fasynchronous-unwind-tables
@@ -263,7 +264,7 @@ tests = tst-attr1 tst-attr2 tst-attr3 tst-default-attr \
 	tst-key1 tst-key2 tst-key3 tst-key4 \
 	tst-sem1 tst-sem2 tst-sem3 tst-sem4 tst-sem5 tst-sem6 tst-sem7 \
 	tst-sem8 tst-sem9 tst-sem10 tst-sem14 \
-	tst-sem15 tst-sem16 \
+	tst-sem15 tst-sem16 tst-sem17 \
 	tst-barrier1 tst-barrier2 tst-barrier3 tst-barrier4 \
 	tst-align tst-align3 \
 	tst-basic1 tst-basic2 tst-basic3 tst-basic4 tst-basic5 tst-basic6 \
diff --git a/nptl/Versions b/nptl/Versions
index e7f691d..cd1806c 100644
--- a/nptl/Versions
+++ b/nptl/Versions
@@ -277,6 +277,10 @@ libpthread {
     cnd_timedwait; cnd_wait; tss_create; tss_delete; tss_get; tss_set;
   }
 
+  GLIBC_2.30 {
+    sem_clockwait;
+  }
+
   GLIBC_PRIVATE {
     __pthread_initialize_minimal;
     __pthread_clock_gettime; __pthread_clock_settime;
diff --git a/nptl/sem_clockwait.c b/nptl/sem_clockwait.c
new file mode 100644
index 0000000..c0cd667
--- /dev/null
+++ b/nptl/sem_clockwait.c
@@ -0,0 +1,45 @@
+/* sem_clockwait -- wait on a semaphore with timeout using
+   the specified clock.
+
+   Copyright (C) 2003-2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "sem_waitcommon.c"
+
+int
+sem_clockwait (sem_t *sem, clockid_t clockid,
+	       const struct timespec *abstime)
+{
+  /* Check that supplied clockid is one we support, even if we don't
+     end up waiting. */
+  if (!futex_abstimed_supported_clockid (clockid))
+    {
+      __set_errno (EINVAL);
+      return -1;
+    }
+
+  if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000)
+    {
+      __set_errno (EINVAL);
+      return -1;
+    }
+
+  if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
+    return 0;
+  else
+    return __new_sem_wait_slow ((struct new_sem *) sem, clockid, abstime);
+}
diff --git a/nptl/sem_timedwait.c b/nptl/sem_timedwait.c
index 3dd71ab..0918d8b 100644
--- a/nptl/sem_timedwait.c
+++ b/nptl/sem_timedwait.c
@@ -36,5 +36,6 @@ sem_timedwait (sem_t *sem, const struct timespec *abstime)
   if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
     return 0;
   else
-    return __new_sem_wait_slow((struct new_sem *) sem, abstime);
+    return __new_sem_wait_slow ((struct new_sem *) sem,
+				CLOCK_REALTIME, abstime);
 }
diff --git a/nptl/sem_wait.c b/nptl/sem_wait.c
index 6a2d26b..20a8b9d 100644
--- a/nptl/sem_wait.c
+++ b/nptl/sem_wait.c
@@ -39,7 +39,8 @@ __new_sem_wait (sem_t *sem)
   if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
     return 0;
   else
-    return __new_sem_wait_slow((struct new_sem *) sem, NULL);
+    return __new_sem_wait_slow ((struct new_sem *) sem,
+				CLOCK_REALTIME, NULL);
 }
 versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
 
diff --git a/nptl/sem_waitcommon.c b/nptl/sem_waitcommon.c
index 425d040..cad56e9 100644
--- a/nptl/sem_waitcommon.c
+++ b/nptl/sem_waitcommon.c
@@ -103,19 +103,19 @@ __sem_wait_cleanup (void *arg)
    users don't seem to need it.  */
 static int
 __attribute__ ((noinline))
-do_futex_wait (struct new_sem *sem, const struct timespec *abstime)
+do_futex_wait (struct new_sem *sem, clockid_t clockid,
+	       const struct timespec *abstime)
 {
   int err;
 
 #if __HAVE_64B_ATOMICS
   err = futex_abstimed_wait_cancelable (
       (unsigned int *) &sem->data + SEM_VALUE_OFFSET, 0,
-      CLOCK_REALTIME, abstime,
+      clockid, abstime,
       sem->private);
 #else
   err = futex_abstimed_wait_cancelable (&sem->value, SEM_NWAITERS_MASK,
-					CLOCK_REALTIME, abstime,
-					sem->private);
+					clockid, abstime, sem->private);
 #endif
 
   return err;
@@ -162,7 +162,8 @@ __new_sem_wait_fast (struct new_sem *sem, int definitive_result)
 /* Slow path that blocks.  */
 static int
 __attribute__ ((noinline))
-__new_sem_wait_slow (struct new_sem *sem, const struct timespec *abstime)
+__new_sem_wait_slow (struct new_sem *sem, clockid_t clockid,
+		     const struct timespec *abstime)
 {
   int err = 0;
 
@@ -180,7 +181,7 @@ __new_sem_wait_slow (struct new_sem *sem, const struct timespec *abstime)
       /* If there is no token available, sleep until there is.  */
       if ((d & SEM_VALUE_MASK) == 0)
 	{
-	  err = do_futex_wait (sem, abstime);
+	  err = do_futex_wait (sem, clockid, abstime);
 	  /* A futex return value of 0 or EAGAIN is due to a real or spurious
 	     wake-up, or due to a change in the number of tokens.  We retry in
 	     these cases.
@@ -281,7 +282,7 @@ __new_sem_wait_slow (struct new_sem *sem, const struct timespec *abstime)
 	  if ((v >> SEM_VALUE_SHIFT) == 0)
 	    {
 	      /* See __HAVE_64B_ATOMICS variant.  */
-	      err = do_futex_wait(sem, abstime);
+	      err = do_futex_wait (sem, clockid, abstime);
 	      if (err == ETIMEDOUT || err == EINTR)
 		{
 		  __set_errno (err);
diff --git a/nptl/tst-sem13.c b/nptl/tst-sem13.c
index 1560e91..0f76100 100644
--- a/nptl/tst-sem13.c
+++ b/nptl/tst-sem13.c
@@ -5,9 +5,14 @@
 #include <pthread.h>
 #include <internaltypes.h>
 
+/* A bogus clock value that tells run_test to use
+   sem_timedwait rather than sem_clockwait */
+#define	CLOCK_USE_TIMEDWAIT (-1)
+
+typedef int (*waitfn_t)(sem_t *, struct timespec *);
 
 static int
-do_test (void)
+do_test_wait (waitfn_t waitfn, const char *fnname)
 {
   union
   {
@@ -23,14 +28,14 @@ do_test (void)
 
   struct timespec ts = { 0, 1000000001 };	/* Invalid.  */
   errno = 0;
-  if (sem_timedwait (&u.s, &ts) >= 0)
+  if (waitfn (&u.s, &ts) >= 0)
     {
-      puts ("sem_timedwait did not fail");
+      printf ("%s did not fail\n", fnname);
       return 1;
     }
   if (errno != EINVAL)
     {
-      perror ("sem_timedwait did not fail with EINVAL");
+      printf ("%s did not fail with EINVAL: %m\n", fnname);
       return 1;
     }
 #if __HAVE_64B_ATOMICS
@@ -40,21 +45,21 @@ do_test (void)
 #endif
   if (nwaiters != 0)
     {
-      printf ("sem_timedwait modified nwaiters: %d\n", nwaiters);
+      printf ("%s modified nwaiters: %d\n", fnname, nwaiters);
       return 1;
     }
 
   ts.tv_sec = /* Invalid.  */ -2;
   ts.tv_nsec = 0;
   errno = 0;
-  if (sem_timedwait (&u.s, &ts) >= 0)
+  if (waitfn (&u.s, &ts) >= 0)
     {
-      puts ("2nd sem_timedwait did not fail");
+      printf ("2nd %s did not fail\n", fnname);
       return 1;
     }
   if (errno != ETIMEDOUT)
     {
-      perror ("2nd sem_timedwait did not fail with ETIMEDOUT");
+      printf ("2nd %s did not fail with ETIMEDOUT\n", fnname);
       return 1;
     }
 #if __HAVE_64B_ATOMICS
@@ -64,12 +69,39 @@ do_test (void)
 #endif
   if (nwaiters != 0)
     {
-      printf ("2nd sem_timedwait modified nwaiters: %d\n", nwaiters);
+      printf ("2nd %s modified nwaiters: %d\n", fnname, nwaiters);
       return 1;
     }
 
   return 0;
 }
 
+int test_sem_timedwait (sem_t *sem, struct timespec *ts)
+{
+  return sem_timedwait (sem, ts);
+}
+
+int test_sem_clockwait_monotonic (sem_t *sem, struct timespec *ts)
+{
+  return sem_clockwait (sem, CLOCK_MONOTONIC, ts);
+}
+
+int test_sem_clockwait_realtime (sem_t *sem, struct timespec *ts)
+{
+  return sem_clockwait (sem, CLOCK_REALTIME, ts);
+}
+
+static int do_test (void)
+{
+  int result = 0;
+  result |= do_test_wait (&test_sem_timedwait,
+			 "sem_timedwait");
+  result |= do_test_wait (&test_sem_clockwait_monotonic,
+			 "sem_clockwait(monotonic)");
+  result |= do_test_wait (&test_sem_clockwait_realtime,
+			 "sem_clockwait(realtime)");
+  return result;
+}
+
 #define TEST_FUNCTION do_test ()
 #include "../test-skeleton.c"
diff --git a/nptl/tst-sem17.c b/nptl/tst-sem17.c
new file mode 100644
index 0000000..a24ad0f
--- /dev/null
+++ b/nptl/tst-sem17.c
@@ -0,0 +1,57 @@
+/* Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <semaphore.h>
+#include <stdio.h>
+#include <time.h>
+#include <unistd.h>
+#include <sys/time.h>
+
+#define NOT_A_VALID_CLOCK 123456
+
+static int
+do_test (void)
+{
+  sem_t s;
+  struct timespec ts;
+
+  if (sem_init (&s, 0, 1) == -1)
+    {
+      puts ("sem_init failed");
+      return 1;
+    }
+
+  ts.tv_sec = 0;
+  ts.tv_nsec = 0;
+
+  if (sem_clockwait (&s, NOT_A_VALID_CLOCK, &ts) == 0)
+    {
+      puts ("sem_clockwait succeeded with an invalid clock");
+      return 1;
+    }
+  if (errno != EINVAL)
+    {
+      printf ("sem_clockwait yielded incorrect errno for invalid clock: %d\n",
+	      errno);
+      return 1;
+    }
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/nptl/tst-sem5.c b/nptl/tst-sem5.c
index 2149ade..7f1031d 100644
--- a/nptl/tst-sem5.c
+++ b/nptl/tst-sem5.c
@@ -23,13 +23,15 @@
 #include <unistd.h>
 #include <sys/time.h>
 
+/* A bogus clock value that tells run_test to use
+   sem_timedwait rather than sem_clockwait */
+#define	CLOCK_USE_TIMEDWAIT (-1)
 
 static int
-do_test (void)
+do_test_clock (clockid_t clockid)
 {
   sem_t s;
   struct timespec ts;
-  struct timeval tv;
 
   if (sem_init (&s, 0, 1) == -1)
     {
@@ -43,13 +45,8 @@ do_test (void)
       return 1;
     }
 
-  if (gettimeofday (&tv, NULL) != 0)
-    {
-      puts ("gettimeofday failed");
-      return 1;
-    }
-
-  TIMEVAL_TO_TIMESPEC (&tv, &ts);
+  (void) clock_gettime (clockid == CLOCK_USE_TIMEDWAIT
+			? CLOCK_REALTIME : clockid, &ts);
 
   /* We wait for half a second.  */
   ts.tv_nsec += 500000000;
@@ -60,7 +57,9 @@ do_test (void)
     }
 
   errno = 0;
-  if (TEMP_FAILURE_RETRY (sem_timedwait (&s, &ts)) != -1)
+  if (TEMP_FAILURE_RETRY ((clockid == CLOCK_USE_TIMEDWAIT)
+			  ? sem_timedwait (&s, &ts)
+			  : sem_clockwait (&s, clockid, &ts)) != -1)
     {
       puts ("sem_timedwait succeeded");
       return 1;
@@ -73,7 +72,8 @@ do_test (void)
     }
 
   struct timespec ts2;
-  if (clock_gettime (CLOCK_REALTIME, &ts2) != 0)
+  if (clock_gettime (clockid == CLOCK_USE_TIMEDWAIT
+		     ? CLOCK_REALTIME : clockid, &ts2) != 0)
     {
       puts ("clock_gettime failed");
       return 1;
@@ -89,5 +89,13 @@ do_test (void)
   return 0;
 }
 
+static int do_test (void)
+{
+  do_test_clock (CLOCK_USE_TIMEDWAIT);
+  do_test_clock (CLOCK_REALTIME);
+  do_test_clock (CLOCK_MONOTONIC);
+  return 0;
+}
+
 #define TEST_FUNCTION do_test ()
 #include "../test-skeleton.c"
diff --git a/sysdeps/pthread/semaphore.h b/sysdeps/pthread/semaphore.h
index 41ff927..2e68b16 100644
--- a/sysdeps/pthread/semaphore.h
+++ b/sysdeps/pthread/semaphore.h
@@ -59,6 +59,10 @@ extern int sem_wait (sem_t *__sem);
    __THROW.  */
 extern int sem_timedwait (sem_t *__restrict __sem,
 			  const struct timespec *__restrict __abstime);
+
+extern int sem_clockwait (sem_t *__restrict __sem,
+			  clockid_t clock,
+			  const struct timespec *__restrict __abstime);
 #endif
 
 /* Test whether SEM is posted.  */
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/libpthread.abilist b/sysdeps/unix/sysv/linux/x86_64/64/libpthread.abilist
index 931c827..454d340 100644
--- a/sysdeps/unix/sysv/linux/x86_64/64/libpthread.abilist
+++ b/sysdeps/unix/sysv/linux/x86_64/64/libpthread.abilist
@@ -245,6 +245,7 @@ GLIBC_2.3.4 pthread_attr_setaffinity_np F
 GLIBC_2.3.4 pthread_getaffinity_np F
 GLIBC_2.3.4 pthread_setaffinity_np F
 GLIBC_2.3.4 pthread_setschedprio F
+GLIBC_2.30 sem_clockwait F
 GLIBC_2.4 pthread_mutex_consistent_np F
 GLIBC_2.4 pthread_mutex_getprioceiling F
 GLIBC_2.4 pthread_mutex_setprioceiling F
