diff --git a/nova/compute/api.py b/nova/compute/api.py
index 3daba673d141..e9b7b5b9984e 100644
--- a/nova/compute/api.py
+++ b/nova/compute/api.py
@@ -2422,7 +2422,7 @@ class API(base.Base):
             bdms = self.get_instance_bdms(context, instance)
 
         for bdm in bdms:
-            if (block_device.strip_dev(bdm.device_name) ==
+            if (block_device.strip_dev(bdm['device_name']) ==
                 block_device.strip_dev(instance['root_device_name'])):
                 return True
         else: