diff --git a/django_q/brokers/__init__.py b/django_q/brokers/__init__.py
index a8380ee..0d10cac 100644
--- a/django_q/brokers/__init__.py
+++ b/django_q/brokers/__init__.py
@@ -29,6 +29,11 @@ class Broker(object):
         """
         pass
 
+    def lock_size(self):
+        """
+        :return: the number of tasks currently awaiting acknowledgement
+        """
+
     def delete_queue(self):
         """
         Deletes the queue from the broker
diff --git a/django_q/monitor.py b/django_q/monitor.py
index 3671e83..6a3bcf4 100644
--- a/django_q/monitor.py
+++ b/django_q/monitor.py
@@ -83,8 +83,9 @@ def monitor(run_once=False, broker=None):
             # bottom bar
             i += 1
             queue_size = broker.queue_size()
-            if hasattr(broker, 'lock_size'):
-                queue_size = '{}({})'.format(queue_size, broker.lock_size())
+            lock_size = broker.lock_size()
+            if lock_size:
+                queue_size = '{}({})'.format(queue_size, lock_size)
             print(term.move(i, 0) + term.white_on_cyan(term.center(broker.info(), width=col_width * 2)))
             print(term.move(i, 2 * col_width) + term.black_on_cyan(term.center(_('Queued'), width=col_width)))
             print(term.move(i, 3 * col_width) + term.white_on_cyan(term.center(queue_size, width=col_width)))