diff --git a/uncloud/hack/db.py b/uncloud/hack/db.py
index ac643bd..cb5e490 100644
--- a/uncloud/hack/db.py
+++ b/uncloud/hack/db.py
@@ -86,10 +86,23 @@ class DB(object):
         return self._db_clients[0].put(self.realkey(key), value, **kwargs)
 
     @readable_errors
-    def increment(key, **kwargs):
-        with self._db_clients[0].lock(key) as lock:
-            value = int(self.get(self.realkey(key), **kwargs))
-            self.set(self.realkey(key), str(value + 1), **kwargs)
+    def increment(self, key, **kwargs):
+        print(self.realkey(key))
+
+
+        print("prelock")
+        lock = self._db_clients[0].lock('/nicohack/foo')
+        print("prelockacq")
+        lock.acquire()
+        print("prelockrelease")
+        lock.release()
+
+        with self._db_clients[0].lock("/nicohack/mac/last_used_index") as lock:
+            print("in lock")
+            pass
+
+#        with self._db_clients[0].lock(self.realkey(key)) as lock:#            value = int(self.get(self.realkey(key), **kwargs))
+#            self.set(self.realkey(key), str(value + 1), **kwargs)
 
 
 if __name__ == '__main__':
diff --git a/uncloud/hack/mac.py b/uncloud/hack/mac.py
index a408103..e7f41a2 100755
--- a/uncloud/hack/mac.py
+++ b/uncloud/hack/mac.py
@@ -48,7 +48,9 @@ class MAC(object):
     def last_used_index(self):
         value = self.db.get("last_used_index")
         if not value:
-            return 0
+            self.db.set("last_used_index", "0")
+            value = self.db.get("last_used_index")
+
         return int(value)
 
     def last_used_mac(self):
@@ -62,7 +64,7 @@ class MAC(object):
     def get_next(self, vmuuid=None, as_int=False):
         last_number = self.last_used_index()
 
-        # FIXME: compare to 48bit minus prefix length
+        # FIXME: compare to 48bit minus prefix length to the power of 2
         if last_number == int('0xffffff', 16):
             raise UncloudException("Exhausted all possible mac addresses - try to free some")
 
@@ -77,6 +79,8 @@ class MAC(object):
         db_entry['index'] = next_number
         db_entry['mac_address'] = next_mac
 
+        # should be one transaction
+        self.db.increment("last_used_index")
         self.db.set("used/{}".format(next_mac),
                     db_entry, as_json=True)