diff --git a/mcop_mt/threads_posix.cpp b/mcop_mt/threads_posix.cpp
index 6fa953c..06920b1 100644
--- a/mcop_mt/threads_posix.cpp
+++ b/mcop_mt/threads_posix.cpp
@@ -59,6 +59,7 @@ protected:
 	pthread_mutex_t mutex;
 
 #ifdef PTHREAD_DEBUG
+	bool have_owner;
 	pthread_t owner;
 #endif
 
@@ -67,20 +68,21 @@ public:
 	{
 		pthread_mutex_init(&mutex, 0);
 #ifdef PTHREAD_DEBUG
-		owner = 0;
+		have_owner = false;
 #endif
 	}
 	void lock()
 	{
 #ifdef PTHREAD_DEBUG
 		pthread_t self = pthread_self();
-		arts_assert(owner != self);
+		arts_assert(!have_owner || !pthread_equal(owner, self));
 #endif
 
 		pthread_mutex_lock(&mutex);
 
 #ifdef PTHREAD_DEBUG
-		arts_assert(!owner);
+		arts_assert(!have_owner);
+		have_owner = true;
 		owner = self;
 #endif
 	}
@@ -88,7 +90,7 @@ public:
 	{
 #ifdef PTHREAD_DEBUG
 		pthread_t self = pthread_self();
-		arts_assert(owner != self);
+		arts_assert(!have_owner || !pthread_equal(owner, self));
 #endif
 
 		int result = pthread_mutex_trylock(&mutex);
@@ -96,7 +98,8 @@ public:
 #ifdef PTHREAD_DEBUG
 		if(result == 0)
 		{
-			arts_assert(!owner);
+			arts_assert(!have_owner);
+			have_owner = true;
 			owner = self;
 		}
 #endif
@@ -105,8 +108,8 @@ public:
 	void unlock()
 	{
 #ifdef PTHREAD_DEBUG
-		arts_assert(owner == pthread_self());
-		owner = 0;
+		arts_assert(have_owner && pthread_equal(owner, pthread_self()));
+		have_owner = false;
 #endif
 
 		pthread_mutex_unlock(&mutex);
@@ -117,6 +120,7 @@ class RecMutex_impl : public Arts::Mutex_impl {
 protected:
 	friend class ThreadCondition_impl;
 	pthread_mutex_t mutex;
+	bool have_owner;
 	pthread_t owner;
 	int count;
 
@@ -124,19 +128,20 @@ public:
 	RecMutex_impl()
 	{
 		pthread_mutex_init(&mutex, 0);
-		owner = 0;
+		have_owner = false;
 		count = 0;
 	}
 	void lock()
 	{
 		pthread_t self = pthread_self();
-		if(owner != self)
+		if(!have_owner || !pthread_equal(owner, self))
 		{
 			pthread_mutex_lock(&mutex);
 #ifdef PTHREAD_DEBUG
 			arts_assert(count == 0);
-			arts_assert(!owner);
+			arts_assert(!have_owner);
 #endif
+			have_owner = true;
 			owner = self;
 		}
 		count++;
@@ -144,7 +149,7 @@ public:
 	bool tryLock()
 	{
 		pthread_t self = pthread_self();
-		if(owner != self)
+		if(!have_owner || !pthread_equal(owner, self))
 		{
 			int result = pthread_mutex_trylock(&mutex);
 			if(result != 0)
@@ -152,8 +157,9 @@ public:
 
 #ifdef PTHREAD_DEBUG
 			arts_assert(count == 0);
-			arts_assert(!owner);
+			arts_assert(!have_owner);
 #endif
+			have_owner = true;
 			owner = self;
 		}
 		count++;
@@ -162,14 +168,14 @@ public:
 	void unlock()
 	{
 #ifdef PTHREAD_DEBUG
-		arts_assert(owner == pthread_self());
+		arts_assert(have_owner && pthread_equal(owner, pthread_self()));
 		arts_assert(count > 0);
 #endif
 
 		count--;
 		if(count == 0)
 		{
-			owner = 0;
+			have_owner = false;
 			pthread_mutex_unlock(&mutex);
 		}
 	}
@@ -230,14 +236,15 @@ public:
 	void wait(Arts::Mutex_impl *mutex) {
 #ifdef PTHREAD_DEBUG
 		pthread_t self = pthread_self();
-		arts_assert(((Mutex_impl *)mutex)->owner == self);
-		((Mutex_impl *)mutex)->owner = 0;
+		arts_assert(((Mutex_impl *)mutex)->have_owner && pthread_equal(((Mutex_impl *)mutex)->owner, self));
+		((Mutex_impl *)mutex)->have_owner = false;
 #endif
 
 		pthread_cond_wait(&cond, &((Mutex_impl*)mutex)->mutex);
 
 #ifdef PTHREAD_DEBUG
-		arts_assert(((Mutex_impl *)mutex)->owner == 0);
+		arts_assert(!((Mutex_impl *)mutex)->have_owner);
+		((Mutex_impl *)mutex)->have_owner = true;
 		((Mutex_impl *)mutex)->owner = self;
 #endif
 	}