diff --git a/django/contrib/gis/db/backends/oracle/operations.py b/django/contrib/gis/db/backends/oracle/operations.py
index 84217c331b..628018320b 100644
--- a/django/contrib/gis/db/backends/oracle/operations.py
+++ b/django/contrib/gis/db/backends/oracle/operations.py
@@ -78,7 +78,7 @@ class OracleOperations(DatabaseOperations, BaseSpatialOperations):
 
     name = 'oracle'
     oracle = True
-    valid_aggregates = dict([(a, None) for a in ('Union', 'Extent')])
+    valid_aggregates = {'Union', 'Extent'}
 
     Adapter = OracleSpatialAdapter
     Adaptor = Adapter # Backwards-compatibility alias.
diff --git a/django/contrib/gis/db/backends/postgis/operations.py b/django/contrib/gis/db/backends/postgis/operations.py
index 84dbda3239..3863bea992 100644
--- a/django/contrib/gis/db/backends/postgis/operations.py
+++ b/django/contrib/gis/db/backends/postgis/operations.py
@@ -56,6 +56,7 @@ class PostGISSphereDistance(PostGISDistance):
 class PostGISRelate(PostGISFunctionParam):
     "For PostGIS Relate(<geom>, <pattern>) calls."
     pattern_regex = re.compile(r'^[012TF\*]{9}$')
+
     def __init__(self, prefix, pattern):
         if not self.pattern_regex.match(pattern):
             raise ValueError('Invalid intersection matrix pattern "%s".' % pattern)
@@ -68,8 +69,7 @@ class PostGISOperations(DatabaseOperations, BaseSpatialOperations):
     postgis = True
     geom_func_prefix = 'ST_'
     version_regex = re.compile(r'^(?P<major>\d)\.(?P<minor1>\d)\.(?P<minor2>\d+)')
-    valid_aggregates = dict([(k, None) for k in
-                             ('Collect', 'Extent', 'Extent3D', 'MakeLine', 'Union')])
+    valid_aggregates = {'Collect', 'Extent', 'Extent3D', 'MakeLine', 'Union'}
 
     Adapter = PostGISAdapter
     Adaptor = Adapter # Backwards-compatibility alias.
diff --git a/django/contrib/gis/db/backends/spatialite/operations.py b/django/contrib/gis/db/backends/spatialite/operations.py
index 4281cafa23..9037240e64 100644
--- a/django/contrib/gis/db/backends/spatialite/operations.py
+++ b/django/contrib/gis/db/backends/spatialite/operations.py
@@ -56,7 +56,7 @@ class SpatiaLiteOperations(DatabaseOperations, BaseSpatialOperations):
     name = 'spatialite'
     spatialite = True
     version_regex = re.compile(r'^(?P<major>\d)\.(?P<minor1>\d)\.(?P<minor2>\d+)')
-    valid_aggregates = dict([(k, None) for k in ('Extent', 'Union')])
+    valid_aggregates = {'Extent', 'Union'}
 
     Adapter = SpatiaLiteAdapter
     Adaptor = Adapter # Backwards-compatibility alias.