diff --git a/nailgun/nailgun/api/v1/handlers/cluster.py b/nailgun/nailgun/api/v1/handlers/cluster.py
index 7ceefa99e4..bd24089a15 100644
--- a/nailgun/nailgun/api/v1/handlers/cluster.py
+++ b/nailgun/nailgun/api/v1/handlers/cluster.py
@@ -570,14 +570,10 @@ class ClusterExtensionsHandler(BaseHandler):
         cluster = self._get_cluster_obj(cluster_id)
         # TODO(agordeev): web.py does not support parsing of array arguments
         # in the queryset so we specify the input as comma-separated list
-        extension_names = list(self.get_param_as_set('extension_names',
-                                                     default=[]))
+        extension_names = self.get_param_as_set('extension_names', default=[])
 
-        try:
-            data = self.validator.validate_delete(extension_names,
-                                                  cluster)
-        except errors.CannotFindExtension as exc:
-            raise self.http(400, exc.message)
+        data = self.checked_data(self.validator.validate_delete,
+                                 data=extension_names, cluster=cluster)
 
         remove_extensions_from_object(cluster, data)
         raise self.http(204)
diff --git a/nailgun/nailgun/api/v1/validators/extension.py b/nailgun/nailgun/api/v1/validators/extension.py
index 6209f1ec61..40f3724235 100644
--- a/nailgun/nailgun/api/v1/validators/extension.py
+++ b/nailgun/nailgun/api/v1/validators/extension.py
@@ -39,7 +39,7 @@ class ExtensionValidator(BasicValidator):
 
     @classmethod
     def validate_delete(cls, extension_names, cluster):
-        not_found_extensions = set(extension_names) - set(cluster.extensions)
+        not_found_extensions = extension_names - set(cluster.extensions)
         if not_found_extensions:
             raise errors.CannotFindExtension(
                 "No such extensions to disable: {0}".format(
diff --git a/nailgun/nailgun/test/unit/test_extensions.py b/nailgun/nailgun/test/unit/test_extensions.py
index 84ee7841db..cafe74d1e4 100644
--- a/nailgun/nailgun/test/unit/test_extensions.py
+++ b/nailgun/nailgun/test/unit/test_extensions.py
@@ -247,7 +247,7 @@ class TestExtensionValidator(BaseTestCase):
         cluster = mock.Mock()
         cluster.extensions = global_exts
 
-        ExtensionValidator.validate_delete(global_exts[:2], cluster)
+        ExtensionValidator.validate_delete(set(global_exts[:2]), cluster)
 
     def test_invalid_delete_extensions(self):
         global_exts = 'volume_manager', 'bareon', 'ultralogger'
@@ -257,7 +257,7 @@ class TestExtensionValidator(BaseTestCase):
 
         with self.assertRaisesRegexp(errors.CannotFindExtension,
                                      'No such extensions to disable: invalid'):
-                ExtensionValidator.validate_delete(data, cluster)
+                ExtensionValidator.validate_delete(set(data), cluster)
 
     def test_validate_extensions(self):
         global_exts = 'volume_manager', 'bareon', 'ultralogger'