diff --git a/django_q/brokers/aws_sqs.py b/django_q/brokers/aws_sqs.py
index 2334c20..111e631 100644
--- a/django_q/brokers/aws_sqs.py
+++ b/django_q/brokers/aws_sqs.py
@@ -27,6 +27,9 @@ class Sqs(Broker):
     def queue_size(self):
         return int(self.queue.attributes['ApproximateNumberOfMessages'])
 
+    def lock_size(self):
+        return int(self.queue.attributes['ApproximateNumberOfMessagesNotVisible'])
+
     def delete(self, task_id):
         message = self.sqs.Message(self.queue.url, task_id)
         message.delete()
diff --git a/django_q/tests/test_brokers.py b/django_q/tests/test_brokers.py
index 6222e34..150adfd 100644
--- a/django_q/tests/test_brokers.py
+++ b/django_q/tests/test_brokers.py
@@ -216,6 +216,7 @@ def test_sqs():
         broker.acknowledge(task[0])
     # duplicate acknowledge
     broker.acknowledge(task[0])
+    assert broker.lock_size() == 0
     # delete queue
     broker.enqueue('test')
     broker.purge_queue()
diff --git a/docs/brokers.rst b/docs/brokers.rst
index e0de123..429419b 100644
--- a/docs/brokers.rst
+++ b/docs/brokers.rst
@@ -129,6 +129,11 @@ You can override this class if you want to contribute and support your own broke
 
       Returns the amount of messages in the brokers queue.
 
+   .. py:method:: lock_size()
+
+      Optional method that returns the number of messages currently awaiting acknowledgement.
+      Only implemented on brokers that support it.
+
    .. py:method:: ping()
 
       Returns True if the broker can be reached.