diff --git a/lib/libthr/thread/thr_mutex.c b/lib/libthr/thread/thr_mutex.c
index ee615c3648b5..e47fb60634e8 100644
--- a/lib/libthr/thread/thr_mutex.c
+++ b/lib/libthr/thread/thr_mutex.c
@@ -301,11 +301,16 @@ __pthread_mutex_trylock(pthread_mutex_t *mutex)
 	return (ret);
 }
 
+/*
+ * Libc internal.
+ */
 int
 _pthread_mutex_trylock(pthread_mutex_t *mutex)
 {
 	int	ret = 0;
 
+	_thread_sigblock();
+
 	if (mutex == NULL)
 		ret = EINVAL;
 
@@ -317,6 +322,9 @@ _pthread_mutex_trylock(pthread_mutex_t *mutex)
 	    (ret = mutex_init(mutex, 1)) == 0)
 		ret = mutex_lock_common(mutex, 1);
 
+	if (ret != 0)
+		_thread_sigunblock();
+
 	return (ret);
 }