diff --git a/qemu-thread-posix.c b/qemu-thread-posix.c
index 6a3d3a1..4ef9c7b 100644
--- a/qemu-thread-posix.c
+++ b/qemu-thread-posix.c
@@ -122,36 +122,106 @@
 {
     int rc;
 
+#if defined(__OpenBSD__) || defined(__APPLE__) || defined(__NetBSD__)
+    rc = pthread_mutex_init(&sem->lock, NULL);
+    if (rc != 0) {
+        error_exit(rc, __func__);
+    }
+    rc = pthread_cond_init(&sem->cond, NULL);
+    if (rc != 0) {
+        error_exit(rc, __func__);
+    }
+    if (init < 0) {
+        error_exit(EINVAL, __func__);
+    }
+    sem->count = init;
+#else
     rc = sem_init(&sem->sem, 0, init);
     if (rc < 0) {
         error_exit(errno, __func__);
     }
+#endif
 }
 
 void qemu_sem_destroy(QemuSemaphore *sem)
 {
     int rc;
 
+#if defined(__OpenBSD__) || defined(__APPLE__) || defined(__NetBSD__)
+    rc = pthread_cond_destroy(&sem->cond);
+    if (rc < 0) {
+        error_exit(rc, __func__);
+    }
+    rc = pthread_mutex_destroy(&sem->lock);
+    if (rc < 0) {
+        error_exit(rc, __func__);
+    }
+#else
     rc = sem_destroy(&sem->sem);
     if (rc < 0) {
         error_exit(errno, __func__);
     }
+#endif
 }
 
 void qemu_sem_post(QemuSemaphore *sem)
 {
     int rc;
 
+#if defined(__OpenBSD__) || defined(__APPLE__) || defined(__NetBSD__)
+    pthread_mutex_lock(&sem->lock);
+    if (sem->count == INT_MAX) {
+        rc = EINVAL;
+    } else if (sem->count++ < 0) {
+        rc = pthread_cond_signal(&sem->cond);
+    } else {
+        rc = 0;
+    }
+    pthread_mutex_unlock(&sem->lock);
+    if (rc != 0) {
+        error_exit(rc, __func__);
+    }
+#else
     rc = sem_post(&sem->sem);
     if (rc < 0) {
         error_exit(errno, __func__);
     }
+#endif
+}
+
+static void compute_abs_deadline(struct timespec *ts, int ms)
+{
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    ts->tv_nsec = tv.tv_usec * 1000 + (ms % 1000) * 1000000;
+    ts->tv_sec = tv.tv_sec + ms / 1000;
+    if (ts->tv_nsec >= 1000000000) {
+        ts->tv_sec++;
+        ts->tv_nsec -= 1000000000;
+    }
 }
 
 int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
 {
     int rc;
+    struct timespec ts;
 
+#if defined(__OpenBSD__) || defined(__APPLE__) || defined(__NetBSD__)
+    compute_abs_deadline(&ts, ms);
+    pthread_mutex_lock(&sem->lock);
+    --sem->count;
+    while (sem->count < 0) {
+        rc = pthread_cond_timedwait(&sem->cond, &sem->lock, &ts);
+        if (rc == ETIMEDOUT) {
+            break;
+        }
+        if (rc != 0) {
+            error_exit(rc, __func__);
+        }
+    }
+    pthread_mutex_unlock(&sem->lock);
+    return (rc == ETIMEDOUT ? -1 : 0);
+#else
     if (ms <= 0) {
         /* This is cheaper than sem_timedwait.  */
         do {
@@ -161,15 +231,7 @@
             return -1;
         }
     } else {
-        struct timeval tv;
-        struct timespec ts;
-        gettimeofday(&tv, NULL);
-        ts.tv_nsec = tv.tv_usec * 1000 + (ms % 1000) * 1000000;
-        ts.tv_sec = tv.tv_sec + ms / 1000;
-        if (ts.tv_nsec >= 1000000000) {
-            ts.tv_sec++;
-            ts.tv_nsec -= 1000000000;
-        }
+        compute_abs_deadline(&ts, ms);
         do {
             rc = sem_timedwait(&sem->sem, &ts);
         } while (rc == -1 && errno == EINTR);
@@ -181,10 +243,19 @@
         error_exit(errno, __func__);
     }
     return 0;
+#endif
 }
 
 void qemu_sem_wait(QemuSemaphore *sem)
 {
+#if defined(__OpenBSD__) || defined(__APPLE__) || defined(__NetBSD__)
+    pthread_mutex_lock(&sem->lock);
+    --sem->count;
+    while (sem->count < 0) {
+        pthread_cond_wait(&sem->cond, &sem->lock);
+    }
+    pthread_mutex_unlock(&sem->lock);
+#else
     int rc;
 
     do {
@@ -193,6 +264,7 @@
     if (rc < 0) {
         error_exit(errno, __func__);
     }
+#endif
 }
 
 void qemu_thread_create(QemuThread *thread,