diff --git a/buildman/manager/executor.py b/buildman/manager/executor.py
index e030419a5..f6966debd 100644
--- a/buildman/manager/executor.py
+++ b/buildman/manager/executor.py
@@ -161,7 +161,7 @@ class EC2Executor(BuilderExecutor):
             'BuildUUID': build_uuid,
         }))
       except boto.exception.EC2ResponseError as ec2e:
-        if ec2e.error_code == 404:
+        if ec2e.error_code == 'InvalidInstanceID.NotFound':
           if i < _TAG_RETRY_COUNT - 1:
             logger.warning('Failed to write EC2 tags (attempt #%s)', i)
             yield From(trollius.sleep(_TAG_RETRY_SLEEP))
@@ -179,7 +179,7 @@ class EC2Executor(BuilderExecutor):
       ec2_conn = self._get_conn()
       terminated_instances = yield From(ec2_conn.terminate_instances([builder_id]))
     except boto.exception.EC2ResponseError as ec2e:
-      if ec2e.error_code == 404:
+      if ec2e.error_code == 'InvalidInstanceID.NotFound':
         logger.debug('Instance %s already terminated', builder_id)
         return