diff --git a/src/wormhole/_dilation/inbound.py b/src/wormhole/_dilation/inbound.py
index 2f6ffaf..7adaade 100644
--- a/src/wormhole/_dilation/inbound.py
+++ b/src/wormhole/_dilation/inbound.py
@@ -60,9 +60,9 @@ class Inbound(object):
             return True
         return False
 
-    def update_ack_watermark(self, r):
+    def update_ack_watermark(self, seqnum):
         self._highest_inbound_acked = max(self._highest_inbound_acked,
-                                          r.seqnum)
+                                          seqnum)
 
     def handle_open(self, scid):
         if scid in self._open_subchannels:
diff --git a/src/wormhole/test/dilate/test_inbound.py b/src/wormhole/test/dilate/test_inbound.py
index 392a661..f512575 100644
--- a/src/wormhole/test/dilate/test_inbound.py
+++ b/src/wormhole/test/dilate/test_inbound.py
@@ -27,12 +27,12 @@ class InboundTest(unittest.TestCase):
         self.assertFalse(i.is_record_old(r2))
         self.assertFalse(i.is_record_old(r3))
 
-        i.update_ack_watermark(r1)
+        i.update_ack_watermark(r1.seqnum)
         self.assertTrue(i.is_record_old(r1))
         self.assertFalse(i.is_record_old(r2))
         self.assertFalse(i.is_record_old(r3))
 
-        i.update_ack_watermark(r2)
+        i.update_ack_watermark(r2.seqnum)
         self.assertTrue(i.is_record_old(r1))
         self.assertTrue(i.is_record_old(r2))
         self.assertFalse(i.is_record_old(r3))