diff --git a/src/thread/pthread_mutex_consistent.c b/src/thread/pthread_mutex_consistent.c
index 0db976ab..96b83b52 100644
--- a/src/thread/pthread_mutex_consistent.c
+++ b/src/thread/pthread_mutex_consistent.c
@@ -5,6 +5,6 @@ int pthread_mutex_consistent(pthread_mutex_t *m)
 	if (!(m->_m_type & 8)) return EINVAL;
 	if ((m->_m_lock & 0x7fffffff) != __pthread_self()->tid)
 		return EPERM;
-	m->_m_type -= 8;
+	m->_m_type &= ~8U;
 	return 0;
 }
diff --git a/src/thread/pthread_mutex_trylock.c b/src/thread/pthread_mutex_trylock.c
index f871e9e0..8d256614 100644
--- a/src/thread/pthread_mutex_trylock.c
+++ b/src/thread/pthread_mutex_trylock.c
@@ -19,6 +19,7 @@ int __pthread_mutex_trylock_owner(pthread_mutex_t *m)
 		m->_m_count++;
 		return 0;
 	}
+	if (own == 0x40000000) return ENOTRECOVERABLE;
 
 	self->robust_list.pending = &m->_m_next;
 
@@ -35,16 +36,9 @@ int __pthread_mutex_trylock_owner(pthread_mutex_t *m)
 	self->robust_list.head = &m->_m_next;
 	self->robust_list.pending = 0;
 
-	if (type < 4) return 0;
-
-	if (type >= 8) {
-		m->_m_lock = 0;
-		return ENOTRECOVERABLE;
-	}
-
 	if (own) {
 		m->_m_count = 0;
-		m->_m_type += 8;
+		m->_m_type |= 8;
 		return EOWNERDEAD;
 	}
 
diff --git a/src/thread/pthread_mutex_unlock.c b/src/thread/pthread_mutex_unlock.c
index b4ed3f87..42837516 100644
--- a/src/thread/pthread_mutex_unlock.c
+++ b/src/thread/pthread_mutex_unlock.c
@@ -12,8 +12,6 @@ int pthread_mutex_unlock(pthread_mutex_t *m)
 	int priv = (m->_m_type & 128) ^ 128;
 
 	if (type != PTHREAD_MUTEX_NORMAL) {
-		if (!m->_m_lock)
-			return EPERM;
 		self = __pthread_self();
 		if ((m->_m_lock&0x7fffffff) != self->tid)
 			return EPERM;
@@ -26,7 +24,7 @@ int pthread_mutex_unlock(pthread_mutex_t *m)
 		*(void **)m->_m_prev = m->_m_next;
 		if (m->_m_next) ((void **)m->_m_next)[-1] = m->_m_prev;
 	}
-	cont = a_swap(&m->_m_lock, 0);
+	cont = a_swap(&m->_m_lock, (type & 8) ? 0x40000000 : 0);
 	if (type != PTHREAD_MUTEX_NORMAL && !priv) {
 		self->robust_list.pending = 0;
 		__vm_unlock_impl();