Index: dbus/dbus-threads.c
===================================================================
--- dbus/dbus-threads.c	(revision 651)
+++ dbus/dbus-threads.c	(working copy)
@@ -139,16 +139,17 @@
  * Locks may be recursive if threading implementation initialized
  * recursive locks.
  */
-void
+dbus_bool_t
 _dbus_mutex_lock (DBusMutex *mutex)
 {
   if (mutex) 
     {
       if (thread_functions.recursive_mutex_lock)
-        (* thread_functions.recursive_mutex_lock) (mutex);
+        return (* thread_functions.recursive_mutex_lock) (mutex);
       else if (thread_functions.mutex_lock)
-        (* thread_functions.mutex_lock) (mutex);
+        return (* thread_functions.mutex_lock) (mutex);
     }
+  return TRUE;
 }
 
 /**
@@ -156,16 +157,17 @@
  *
  * @returns #TRUE on success
  */
-void
+dbus_bool_t
 _dbus_mutex_unlock (DBusMutex *mutex)
 {
   if (mutex)
     {
       if (thread_functions.recursive_mutex_unlock)
-        (* thread_functions.recursive_mutex_unlock) (mutex);
+        return (* thread_functions.recursive_mutex_unlock) (mutex);
       else if (thread_functions.mutex_unlock)
-        (* thread_functions.mutex_unlock) (mutex);
+        return (* thread_functions.mutex_unlock) (mutex);
     }
+  return TRUE;
 }
 
 /**
Index: dbus/dbus-threads.h
===================================================================
--- dbus/dbus-threads.h	(revision 651)
+++ dbus/dbus-threads.h	(working copy)
@@ -65,11 +65,11 @@
 /** Locks a recursively-lockable mutex.  Found in #DBusThreadFunctions.
  * Can only fail due to lack of memory.
  */
-typedef void        (* DBusRecursiveMutexLockFunction)   (DBusMutex *mutex);
+typedef dbus_bool_t (* DBusRecursiveMutexLockFunction)   (DBusMutex *mutex);
 /** Unlocks a recursively-lockable mutex.  Found in #DBusThreadFunctions.
  * Can only fail due to lack of memory.
  */
-typedef void        (* DBusRecursiveMutexUnlockFunction) (DBusMutex *mutex);
+typedef dbus_bool_t (* DBusRecursiveMutexUnlockFunction) (DBusMutex *mutex);
 
 /** Creates a new condition variable.  Found in #DBusThreadFunctions.
  * Can only fail (returning #NULL) due to lack of memory.
Index: dbus/dbus-connection.c
===================================================================
--- dbus/dbus-connection.c	(revision 651)
+++ dbus/dbus-connection.c	(working copy)
@@ -63,14 +63,16 @@
 
 #define CONNECTION_LOCK(connection)   do {                                      \
     if (TRACE_LOCKS) { _dbus_verbose ("  LOCK: %s\n", _DBUS_FUNCTION_NAME); }   \
-    _dbus_mutex_lock ((connection)->mutex);                                      \
+    _dbus_assert((connection)->mutex);                                          \
+    _dbus_assert(_dbus_mutex_lock ((connection)->mutex));                       \
     TOOK_LOCK_CHECK (connection);                                               \
   } while (0)
 
 #define CONNECTION_UNLOCK(connection) do {                                              \
     if (TRACE_LOCKS) { _dbus_verbose ("  UNLOCK: %s\n", _DBUS_FUNCTION_NAME);  }        \
     RELEASING_LOCK_CHECK (connection);                                                  \
-    _dbus_mutex_unlock ((connection)->mutex);                                            \
+    _dbus_assert((connection)->mutex);                                                  \
+    _dbus_assert(_dbus_mutex_unlock ((connection)->mutex));                             \
   } while (0)
 
 #define DISPATCH_STATUS_NAME(s)                                            \
Index: dbus/dbus-threads-internal.h
===================================================================
--- dbus/dbus-threads-internal.h	(revision 651)
+++ dbus/dbus-threads-internal.h	(working copy)
@@ -31,8 +31,8 @@
 
 DBusMutex*   _dbus_mutex_new                 (void);
 void         _dbus_mutex_free                (DBusMutex         *mutex);
-void         _dbus_mutex_lock                (DBusMutex         *mutex);
-void         _dbus_mutex_unlock              (DBusMutex         *mutex);
+dbus_bool_t  _dbus_mutex_lock                (DBusMutex         *mutex);
+dbus_bool_t  _dbus_mutex_unlock              (DBusMutex         *mutex);
 void         _dbus_mutex_new_at_location     (DBusMutex        **location_p);
 void         _dbus_mutex_free_at_location    (DBusMutex        **location_p);