diff --git a/doublethink/services.py b/doublethink/services.py
index 8b7885b..1a22af5 100644
--- a/doublethink/services.py
+++ b/doublethink/services.py
@@ -245,8 +245,7 @@ class ServiceRegistry(object):
                                     row,
                                     row['last_heartbeat'] > r.now() - row['heartbeat_interval'] * 3,
                                     False),
-                                row.merge({'last_heartbeat': r.now()}),
-                                candidate),
+                                row, candidate),
                             return_changes='always').run()
             new_val = result['changes'][0]['new_val']
             if all([new_val[k] == candidate[k] for k in candidate
@@ -263,7 +262,6 @@ class ServiceRegistry(object):
         else:
             return None
 
-
     def healthy_service(self, role):
         '''
         Find least loaded healthy service in the registry.