diff --git a/HISTORY.md b/HISTORY.md
index 0231765..85dcfd0 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -1,5 +1,7 @@
 ## master
 
+- [#50](https://github.com/castle/castle-python/pull/50) avoid dict as default parameter
+
 ## 2.3.0 (2019-01-16)
 
 - [#48](https://github.com/castle/castle-python/pull/48) add connection pooling
diff --git a/castle/client.py b/castle/client.py
index 008a9ee..75db2a4 100644
--- a/castle/client.py
+++ b/castle/client.py
@@ -14,20 +14,26 @@
 class Client(object):
 
     @classmethod
-    def from_request(cls, request, options={}):
+    def from_request(cls, request, options=None):
+        if options is None:
+            options = {}
         return cls(
             cls.to_context(request, options),
             cls.to_options(options)
         )
 
     @staticmethod
-    def to_context(request, options={}):
+    def to_context(request, options=None):
+        if options is None:
+            options = {}
         default_context = ContextDefault(
             request, options.get('cookies')).call()
         return ContextMerger.call(default_context, options.get('context', {}))
 
     @staticmethod
-    def to_options(options={}):
+    def to_options(options=None):
+        if options is None:
+            options = {}
         options.setdefault('timestamp', generate_timestamp())
         if 'traits' in options:
             warnings.warn('use user_traits instead of traits key', DeprecationWarning)
@@ -40,7 +46,9 @@ def failover_response_or_raise(options, exception):
             raise exception
         return FailoverResponse(options.get('user_id'), None, exception.__class__.__name__).call()
 
-    def __init__(self, context, options={}):
+    def __init__(self, context, options=None):
+        if options is None:
+            options = {}
         self.do_not_track = options.get('do_not_track', False)
         self.timestamp = options.get('timestamp')
         self.context = context
diff --git a/castle/test/client_test.py b/castle/test/client_test.py
index d1c12d9..9f1618d 100644
--- a/castle/test/client_test.py
+++ b/castle/test/client_test.py
@@ -1,3 +1,4 @@
+import json
 from collections import namedtuple
 import responses
 from castle.test import mock, unittest
@@ -215,3 +216,25 @@ def test_failover_strategy_throw(self):
         with self.assertRaises(Exception):
             Client.failover_response_or_raise(options, Exception())
         configuration.failover_strategy = 'allow'
+
+    @responses.activate
+    def test_timestamps_are_not_global(self):
+        response_text = {'action': 'allow', 'user_id': '1234'}
+        responses.add(
+            responses.POST,
+            'https://api.castle.io/v1/authenticate',
+            json=response_text,
+            status=200
+        )
+        options1 = {'event': '$login.authenticate', 'user_id': '1234'}
+        options2 = {'event': '$login.authenticate', 'user_id': '1234'}
+        client1 = Client.from_request(request())
+        client1.authenticate(options1)
+        self.mock_timestamp.return_value = '2018-01-02T04:04:05.678'
+        client2 = Client.from_request(request())
+        client2.authenticate(options2)
+
+        response_body1 = json.loads(responses.calls[0].request.body)
+        response_body2 = json.loads(responses.calls[1].request.body)
+
+        self.assertNotEqual(response_body1['timestamp'], response_body2['timestamp'])