diff --git a/predicthq/client.py b/predicthq/client.py
index b9aff76..6ddcaf4 100644
--- a/predicthq/client.py
+++ b/predicthq/client.py
@@ -48,10 +48,15 @@ def request(self, method, path, **kwargs):
         try:
             response.raise_for_status()
         except requests.HTTPError:
+            try:
+                error = response.json()
+            except ValueError:
+                error = response.content
+
             if 400 <= response.status_code <= 499:
-                raise ClientError(response.json())
+                raise ClientError(error)
             else:
-                raise ServerError(response.json())
+                raise ServerError(error)
 
         try:
             result = response.json() or None
diff --git a/predicthq/endpoints/v1/events/schemas.py b/predicthq/endpoints/v1/events/schemas.py
index eca2cd0..0956624 100644
--- a/predicthq/endpoints/v1/events/schemas.py
+++ b/predicthq/endpoints/v1/events/schemas.py
@@ -68,8 +68,8 @@ class TopEventsSearchParams(SortableMixin, Model):
 
 class CalendarParams(SearchParams):
 
-    dates = ModelType(DateTimeRange)
     top_events = ModelType(TopEventsSearchParams)
+    view = StringType(choices=('active',))
 
 
 class CalendarDay(Model):
diff --git a/tests/client_tests.py b/tests/client_tests.py
index a218649..4b7d56b 100644
--- a/tests/client_tests.py
+++ b/tests/client_tests.py
@@ -46,14 +46,18 @@ def test_request(self, responses):
             self.client.get("/server-error/")
             self.assertEqual(ctx.exception.message, responses.calls[4].response.json())
 
+        with self.assertRaises(ServerError) as ctx:
+            self.client.get("/no-json/")
+            self.assertEqual(ctx.exception.message, responses.calls[5].response.content)
+
         # Test headers
         self.client.authenticate(client_id='client_id', client_secret='client_secret', scope=['account'])
-        self.assertEqual(responses.calls[5].request.headers['Authorization'], 'Basic Y2xpZW50X2lkOmNsaWVudF9zZWNyZXQ=')
-        self.assertEqual(responses.calls[5].request.headers['Content-Type'], 'application/x-www-form-urlencoded')
+        self.assertEqual(responses.calls[6].request.headers['Authorization'], 'Basic Y2xpZW50X2lkOmNsaWVudF9zZWNyZXQ=')
+        self.assertEqual(responses.calls[6].request.headers['Content-Type'], 'application/x-www-form-urlencoded')
 
         self.client.accounts.self()
-        self.assertEqual(responses.calls[6].request.headers['Authorization'], 'Bearer token123')
-        self.assertEqual(responses.calls[6].request.headers['Accept'], 'application/json')
+        self.assertEqual(responses.calls[7].request.headers['Authorization'], 'Bearer token123')
+        self.assertEqual(responses.calls[7].request.headers['Accept'], 'application/json')
 
     @with_mock_client(request_returns={"result": "value"})
     def test_get(self, client):
diff --git a/tests/endpoints/v1/events_tests.py b/tests/endpoints/v1/events_tests.py
index f2c0337..f8d691f 100644
--- a/tests/endpoints/v1/events_tests.py
+++ b/tests/endpoints/v1/events_tests.py
@@ -46,7 +46,7 @@ def test_count(self, client, responses):
     @with_client()
     @with_mock_responses()
     def test_calendar(self, client, responses):
-        result = client.events.calendar(start__gte="2015-12-24", start__lte="2015-12-26", country="NZ", top_events__limit=1, top_events__sort=["rank"], dates__tz="Pacific/Auckland")
+        result = client.events.calendar(active__gte="2015-12-24", active__lte="2015-12-26", country="NZ", top_events__limit=1, top_events__sort=["rank"], active__tz="Pacific/Auckland")
         self.assertIsInstance(result, CalendarResultSet)
         self.assertEqual(result.count, 60)
         self.assertEqual(3, len(list(result.iter_all())))
diff --git a/tests/fixtures/requests_responses/client_test/test_request.json b/tests/fixtures/requests_responses/client_test/test_request.json
index 417c2e8..e09d2cd 100644
--- a/tests/fixtures/requests_responses/client_test/test_request.json
+++ b/tests/fixtures/requests_responses/client_test/test_request.json
@@ -37,6 +37,14 @@
     "content_type": "application/json",
     "body": {"error": "server error"}
   },
+  {
+    "method": "GET",
+    "match_querystring": true,
+    "url": "/no-json/",
+    "status": 500,
+    "content_type": "text/plain",
+    "body": "server error"
+  },
   {
     "method": "POST",
     "match_querystring": true,