diff --git a/include/pthread_np.h b/include/pthread_np.h
index fdd497030f89..06b2f5fc66c7 100644
--- a/include/pthread_np.h
+++ b/include/pthread_np.h
@@ -53,6 +53,7 @@ int pthread_mutex_getspinloops_np(pthread_mutex_t *mutex, int *count);
 int pthread_mutex_setspinloops_np(pthread_mutex_t *mutex, int count);
 int pthread_mutex_getyieldloops_np(pthread_mutex_t *mutex, int *count);
 int pthread_mutex_setyieldloops_np(pthread_mutex_t *mutex, int count);
+int pthread_mutex_islocked_np(pthread_mutex_t *mutex);
 int pthread_single_np(void);
 void pthread_suspend_all_np(void);
 int pthread_suspend_np(pthread_t);
diff --git a/lib/libthr/pthread.map b/lib/libthr/pthread.map
index c6e146b6dafe..dfd6c00590e4 100644
--- a/lib/libthr/pthread.map
+++ b/lib/libthr/pthread.map
@@ -395,3 +395,18 @@ global:
 local:
 	*;
 };
+
+FBSD_1.1 {
+global:
+	pthread_mutex_islocked_np;
+local:
+	*;
+} FBSD_1.0;
+
+FBSDprivate_1.1 {
+global:
+	_pthread_mutex_islocked_np;
+local:
+	*;
+} FBSDprivate_1.0;
+
diff --git a/lib/libthr/thread/thr_mutex.c b/lib/libthr/thread/thr_mutex.c
index 6a977612a04e..032f2e34371d 100644
--- a/lib/libthr/thread/thr_mutex.c
+++ b/lib/libthr/thread/thr_mutex.c
@@ -87,6 +87,7 @@ int	__pthread_mutex_setspinloops_np(pthread_mutex_t *mutex, int count);
 int	_pthread_mutex_setyieldloops_np(pthread_mutex_t *mutex, int count);
 int	_pthread_mutex_getyieldloops_np(pthread_mutex_t *mutex, int *count);
 int	__pthread_mutex_setyieldloops_np(pthread_mutex_t *mutex, int count);
+int	_pthread_mutex_islocked_np(pthread_mutex_t *mutex);
 
 static int	mutex_self_trylock(pthread_mutex_t);
 static int	mutex_self_lock(pthread_mutex_t,
@@ -111,6 +112,7 @@ __weak_reference(_pthread_mutex_getspinloops_np, pthread_mutex_getspinloops_np);
 
 __weak_reference(__pthread_mutex_setyieldloops_np, pthread_mutex_setyieldloops_np);
 __weak_reference(_pthread_mutex_getyieldloops_np, pthread_mutex_getyieldloops_np);
+__weak_reference(_pthread_mutex_islocked_np, pthread_mutex_islocked_np);
 
 static int
 mutex_init(pthread_mutex_t *mutex,
@@ -863,3 +865,17 @@ __pthread_mutex_setyieldloops_np(pthread_mutex_t *mutex, int count)
 	(*mutex)->m_yieldloops = count;
 	return (0);
 }
+
+int
+_pthread_mutex_islocked_np(pthread_mutex_t *mutex)
+{
+	struct pthread *curthread = _get_curthread();
+	int ret;
+
+	if (__predict_false(*mutex == NULL)) {
+		ret = init_static(curthread, mutex);
+		if (__predict_false(ret))
+			return (ret);
+	}
+	return ((*mutex)->m_qe.tqe_prev != NULL);
+}