diff --git a/buildman/manager/executor.py b/buildman/manager/executor.py
index a3cd4981b..e82ecf672 100644
--- a/buildman/manager/executor.py
+++ b/buildman/manager/executor.py
@@ -118,12 +118,12 @@ class EC2Executor(BuilderExecutor):
     elif len(reservation.instances) != 1:
       raise ExecutorException('EC2 started wrong number of instances!')
 
-    return reservation.instances[0]
+    return reservation.instances[0].id
 
   def stop_builder(self, builder_id):
     ec2_conn = self._get_conn()
-    stopped_instances = ec2_conn.stop_instances([builder_id], force=True)
-    if builder_id not in stopped_instances:
+    stopped_instance_ids = [si.id for si in ec2_conn.stop_instances([builder_id], force=True)]
+    if builder_id not in stopped_instance_ids:
       raise ExecutorException('Unable to stop instance: %s' % builder_id)
 
 class PopenExecutor(BuilderExecutor):