--- a/taskcluster/taskgraph/util/attributes.py
+++ b/taskcluster/taskgraph/util/attributes.py
@@ -1,26 +1,26 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 import re
 
 
-INTEGRATION_PROJECTS = set([
+INTEGRATION_PROJECTS = {
     'mozilla-inbound',
     'autoland',
-])
+}
 
-RELEASE_PROJECTS = set([
+RELEASE_PROJECTS = {
     'mozilla-central',
     'mozilla-aurora',
     'mozilla-beta',
     'mozilla-release',
-])
+}
 
 
 def attrmatch(attributes, **kwargs):
     """Determine whether the given set of task attributes matches.  The
     conditions are given as keyword arguments, where each keyword names an
     attribute.  The keyword value can be a literal, a set, or a callable.  A
     literal must match the attribute exactly.  Given a set, the attribute value
     must be in the set.  A callable is called with the attribute value.  If an