diff --git a/ceilometer/api/controllers/v2/events.py b/ceilometer/api/controllers/v2/events.py
index 23b4ba9a..bb2120c5 100644
--- a/ceilometer/api/controllers/v2/events.py
+++ b/ceilometer/api/controllers/v2/events.py
@@ -187,13 +187,13 @@ def _event_query_to_event_filter(q):
         if not i.op:
             i.op = 'eq'
         elif i.op not in base.operation_kind:
-            error = (_('operator %(operator)s is not supported. the supported'
+            error = (_('Operator %(operator)s is not supported. The supported'
                        ' operators are: %(supported)s') %
                      {'operator': i.op, 'supported': base.operation_kind})
             raise base.ClientSideError(error)
         if i.field in evt_model_filter:
             if i.op != 'eq':
-                error = (_('operator %(operator)s is not supported. Only'
+                error = (_('Operator %(operator)s is not supported. Only'
                            ' equality operator is available for field'
                            ' %(field)s') %
                          {'operator': i.op, 'field': i.field})
diff --git a/ceilometer/tests/functional/api/v2/test_event_scenarios.py b/ceilometer/tests/functional/api/v2/test_event_scenarios.py
index abe743c3..0ed96b75 100644
--- a/ceilometer/tests/functional/api/v2/test_event_scenarios.py
+++ b/ceilometer/tests/functional/api/v2/test_event_scenarios.py
@@ -217,7 +217,7 @@ class TestEventAPI(EventTestBase):
                                  'op': 'whats-up'}],
                              expect_errors=True)
         self.assertEqual(400, resp.status_code)
-        self.assertEqual("operator whats-up is not supported. the "
+        self.assertEqual("Operator whats-up is not supported. The "
                          "supported operators are: (\'lt\', \'le\', "
                          "\'eq\', \'ne\', \'ge\', \'gt\')",
                          resp.json['error_message']['faultstring'])