Index: lib/libthr/thread/thr_rwlock.c
===================================================================
--- lib/libthr/thread/thr_rwlock.c	(revision 197623)
+++ lib/libthr/thread/thr_rwlock.c	(working copy)
@@ -26,15 +26,22 @@
  * $FreeBSD$
  */
 
+#include <assert.h>
 #include <errno.h>
 #include <limits.h>
 #include <stdlib.h>
 
+#include <sys/umtx.h>
+
 #include "namespace.h"
 #include <pthread.h>
 #include "un-namespace.h"
 #include "thr_private.h"
 
+#ifdef NDEBUG
+#error "This should compiled with debugging options on"
+#endif
+
 __weak_reference(_pthread_rwlock_destroy, pthread_rwlock_destroy);
 __weak_reference(_pthread_rwlock_init, pthread_rwlock_init);
 __weak_reference(_pthread_rwlock_rdlock, pthread_rwlock_rdlock);
@@ -74,6 +81,11 @@
 		prwlock = *rwlock;
 		*rwlock = NULL;
 
+		assert(prwlock->owner == NULL);
+		assert(prwlock->lock.rw_state == UMUTEX_UNOWNED);
+		assert(prwlock->lock.rw_flags == 0x00);
+		assert(prwlock->lock.rw_blocked_readers == 0);
+		assert(prwlock->lock.rw_blocked_writers == 0);
 		free(prwlock);
 		ret = 0;
 	}