diff --git a/repos/libports/src/lib/libc/pthread.cc b/repos/libports/src/lib/libc/pthread.cc
index 494cf0d439..cefa5f8e7b 100644
--- a/repos/libports/src/lib/libc/pthread.cc
+++ b/repos/libports/src/lib/libc/pthread.cc
@@ -505,6 +505,15 @@ struct Libc::Pthread_mutex_recursive : pthread_mutex
 };
 
 
+/*
+ * The pthread_cond implementation uses the POSIX semaphore API
+ * internally that does not have means to set the clock. For this
+ * reason the private 'sem_set_clock' function is introduced,
+ * see 'semaphore.cc' for the implementation.
+*/
+extern "C" int sem_set_clock(sem_t *sem, clockid_t clock_id);
+
+
 extern "C" {
 
 	/* Thread */
@@ -879,11 +888,16 @@ extern "C" {
 		sem_t           signal_sem;
 		sem_t           handshake_sem;
 
-		pthread_cond() : num_waiters(0), num_signallers(0)
+		pthread_cond(clockid_t clock_id) : num_waiters(0), num_signallers(0)
 		{
 			pthread_mutex_init(&counter_mutex, nullptr);
 			sem_init(&signal_sem, 0, 0);
 			sem_init(&handshake_sem, 0, 0);
+
+			if (sem_set_clock(&signal_sem, clock_id)) {
+				struct Invalid_timedwait_clock { };
+				throw Invalid_timedwait_clock();
+			}
 		}
 
 		~pthread_cond()
@@ -895,12 +909,25 @@ extern "C" {
 	};
 
 
+	struct pthread_cond_attr
+	{
+		clockid_t clock_id { CLOCK_REALTIME };
+	};
+
+
 	int pthread_condattr_init(pthread_condattr_t *attr)
 	{
+		static Mutex condattr_init_mutex { };
+
 		if (!attr)
 			return EINVAL;
 
-		*attr = nullptr;
+		try {
+			Mutex::Guard guard(condattr_init_mutex);
+			Libc::Allocator alloc { };
+			*attr = new (alloc) pthread_cond_attr;
+			return 0;
+		} catch (...) { return ENOMEM; }
 
 		return 0;
 	}
@@ -908,10 +935,13 @@ extern "C" {
 
 	int pthread_condattr_destroy(pthread_condattr_t *attr)
 	{
-		/* assert that the attr was produced by the init no-op */
-		if (!attr || *attr != nullptr)
+		if (!attr)
 			return EINVAL;
 
+		Libc::Allocator alloc { };
+		destroy(alloc, *attr);
+		*attr = nullptr;
+
 		return 0;
 	}
 
@@ -919,11 +949,10 @@ extern "C" {
 	int pthread_condattr_setclock(pthread_condattr_t *attr,
 	                              clockid_t clock_id)
 	{
-		/* assert that the attr was produced by the init no-op */
-		if (!attr || *attr != nullptr)
+		if (!attr)
 			return EINVAL;
 
-		warning(__func__, " not implemented yet");
+		(*attr)->clock_id = clock_id;
 
 		return 0;
 	}
@@ -940,7 +969,8 @@ extern "C" {
 		try {
 			Mutex::Guard guard(cond_init_mutex);
 			Libc::Allocator alloc { };
-			*cond = new (alloc) pthread_cond;
+			*cond = attr && *attr ? new (alloc) pthread_cond((*attr)->clock_id)
+			                      : new (alloc) pthread_cond(CLOCK_REALTIME);
 			return 0;
 		} catch (...) { return ENOMEM; }
 	}
diff --git a/repos/libports/src/lib/libc/semaphore.cc b/repos/libports/src/lib/libc/semaphore.cc
index 85f9e82233..5a55b00cba 100644
--- a/repos/libports/src/lib/libc/semaphore.cc
+++ b/repos/libports/src/lib/libc/semaphore.cc
@@ -64,6 +64,8 @@ struct sem : Genode::Noncopyable
 		int        _count;
 		Mutex      _data_mutex;
 
+		clockid_t  _clock_id { CLOCK_REALTIME };
+
 		/* _data_mutex must be hold when calling the following methods */
 
 		void _append_applicant(Applicant *applicant)
@@ -185,7 +187,7 @@ struct sem : Genode::Noncopyable
 				return 0;
 
 			timespec abs_now;
-			clock_gettime(CLOCK_REALTIME, &abs_now);
+			clock_gettime(_clock_id, &abs_now);
 
 			Libc::uint64_t const timeout_ms =
 				calculate_relative_timeout_ms(abs_now, abs_timeout);
@@ -206,11 +208,31 @@ struct sem : Genode::Noncopyable
 
 			return 0;
 		}
+
+		int set_clock(clockid_t clock_id)
+		{
+			switch (clock_id) {
+			case CLOCK_REALTIME:
+				_clock_id = CLOCK_REALTIME;
+				return 0;
+			case CLOCK_MONOTONIC:
+				_clock_id = CLOCK_MONOTONIC;
+				return 0;
+			default:
+				break;
+			}
+			return -1;
+		}
 };
 
 
 extern "C" {
 
+	int sem_set_clock(sem_t *sem, clockid_t clock_id)
+	{
+		return (*sem)->set_clock(clock_id);
+	}
+
 	int sem_close(sem_t *)
 	{
 		warning(__func__, " not implemented");