diff --git a/repos/libports/src/lib/libc/rwlock.cc b/repos/libports/src/lib/libc/rwlock.cc
index 102939337..f96238e98 100644
--- a/repos/libports/src/lib/libc/rwlock.cc
+++ b/repos/libports/src/lib/libc/rwlock.cc
@@ -91,10 +91,23 @@ extern "C" {
 	{
 	};
 
+	static int rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
+	{
+		static Genode::Lock rwlock_init_lock { };
+
+		if (!rwlock)
+			return EINVAL;
+
+		try {
+			Genode::Lock::Guard g(rwlock_init_lock);
+			*rwlock = new struct pthread_rwlock();
+			return 0;
+		} catch (...) { return ENOMEM; }
+	}
+
 	int pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
 	{
-		*rwlock = new struct pthread_rwlock();
-		return 0;
+		return rwlock_init(rwlock, attr);
 	}
 
 	int pthread_rwlock_destroy(pthread_rwlock_t *rwlock)
@@ -105,12 +118,26 @@ extern "C" {
 
 	int pthread_rwlock_rdlock(pthread_rwlock_t * rwlock)
 	{
+		if (!rwlock)
+			return EINVAL;
+
+		if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
+			if (rwlock_init(rwlock, NULL))
+				return ENOMEM;
+
 		(*rwlock)->rdlock();
 		return 0;
 	}
 
 	int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock)
 	{
+		if (!rwlock)
+			return EINVAL;
+
+		if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
+			if (rwlock_init(rwlock, NULL))
+				return ENOMEM;
+
 		(*rwlock)->wrlock();
 		return 0;
 	}
diff --git a/repos/libports/src/lib/libc/thread.cc b/repos/libports/src/lib/libc/thread.cc
index 0c7b74222..935963eba 100644
--- a/repos/libports/src/lib/libc/thread.cc
+++ b/repos/libports/src/lib/libc/thread.cc
@@ -639,15 +639,26 @@ extern "C" {
 	}
 
 
-	int pthread_cond_init(pthread_cond_t *__restrict cond,
-	                      const pthread_condattr_t *__restrict attr)
+	static int cond_init(pthread_cond_t *__restrict cond,
+	                     const pthread_condattr_t *__restrict attr)
 	{
+		static Genode::Lock cond_init_lock { };
+
 		if (!cond)
 			return EINVAL;
 
-		*cond = new pthread_cond;
+		try {
+			Genode::Lock::Guard g(cond_init_lock);
+			*cond = new pthread_cond;
+			return 0;
+		} catch (...) { return ENOMEM; }
+	}
 
-		return 0;
+
+	int pthread_cond_init(pthread_cond_t *__restrict cond,
+	                      const pthread_condattr_t *__restrict attr)
+	{
+		return cond_init(cond, attr);
 	}
 
 
@@ -710,9 +721,12 @@ extern "C" {
 	{
 		int result = 0;
 
-		if (!cond || !*cond)
+		if (!cond)
 			return EINVAL;
 
+		if (*cond == PTHREAD_COND_INITIALIZER)
+			cond_init(cond, NULL);
+
 		pthread_cond *c = *cond;
 
 		c->counter_lock.lock();