diff --git a/.circleci/config.yml b/.circleci/config.yml
index 87453577..f33121db 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -86,9 +86,8 @@ jobs:
             - run:
                 name: verify typehints
                 command: |
-                  pip install mypy
                   export PATH="/home/circleci/.local/bin:$PATH"
-                  mypy --config-file mypy.ini --python-version 3.5 ldclient/*.py testing/*.py
+                  mypy --config-file mypy.ini ldclient testing
       - store_test_results:
           path: test-reports
       - store_artifacts:
diff --git a/README.md b/README.md
index 80bd937b..5782eff1 100644
--- a/README.md
+++ b/README.md
@@ -46,4 +46,3 @@ We encourage pull requests and other contributions from the community. Check out
     * [docs.launchdarkly.com](https://docs.launchdarkly.com/  "LaunchDarkly Documentation") for our documentation and SDK reference guides
     * [apidocs.launchdarkly.com](https://apidocs.launchdarkly.com/  "LaunchDarkly API Documentation") for our API documentation
     * [blog.launchdarkly.com](https://blog.launchdarkly.com/  "LaunchDarkly Blog Documentation") for the latest product updates
-    * [Feature Flagging Guide](https://github.com/launchdarkly/featureflags/  "Feature Flagging Guide") for best practices and strategies
diff --git a/ldclient/event_processor.py b/ldclient/event_processor.py
index 6bdb7da9..6174f7f2 100644
--- a/ldclient/event_processor.py
+++ b/ldclient/event_processor.py
@@ -3,6 +3,7 @@
 """
 # currently excluded from documentation - see docs/README.md
 
+from calendar import timegm
 from collections import namedtuple
 from email.utils import parsedate
 import errno
@@ -361,7 +362,7 @@ def _handle_response(self, r):
         if server_date_str is not None:
             server_date = parsedate(server_date_str)
             if server_date is not None:
-                timestamp = int(time.mktime(server_date) * 1000)
+                timestamp = int(timegm(server_date) * 1000)
                 self._last_known_past_time = timestamp
         if r.status > 299 and not is_http_error_recoverable(r.status):
             self._disabled = True
diff --git a/mypy.ini b/mypy.ini
index d345df18..e886c085 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,3 +1,2 @@
 [mypy]
-ignore_missing_imports = true
-python_version = 3.5
+ignore_missing_imports = true
\ No newline at end of file
diff --git a/test-requirements.txt b/test-requirements.txt
index d73c173e..1f80fcc7 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -6,4 +6,5 @@ coverage>=4.4
 jsonpickle==0.9.3
 pytest-cov>=2.4.0
 codeclimate-test-reporter>=0.2.1
-pytest-mypy==0.7
\ No newline at end of file
+pytest-mypy==0.7
+mypy==0.800
\ No newline at end of file
diff --git a/testing/test_event_processor.py b/testing/test_event_processor.py
index 77ec05e8..0946b583 100644
--- a/testing/test_event_processor.py
+++ b/testing/test_event_processor.py
@@ -280,6 +280,33 @@ def test_event_can_be_both_tracked_and_debugged():
         check_feature_event(output[2], e, True, user)
         check_summary_event(output[3])
 
+def test_debug_mode_does_not_expire_if_both_client_time_and_server_time_are_before_expiration_time():
+    with DefaultTestProcessor() as ep:
+        # Pick a server time that slightly different from client time
+        server_time = now() + 1000
+
+        # Send and flush an event we don't care about, just to set the last server time
+        mock_http.set_server_time(server_time)
+        ep.send_event({ 'kind': 'identify', 'user': { 'key': 'otherUser' }})
+        flush_and_get_events(ep)
+
+        # Now send an event with debug mode on, with a "debug until" time that is further in
+        # the future than both the client time and the server time
+        debug_until = server_time + 10000
+        e = {
+            'kind': 'feature', 'key': 'flagkey', 'version': 11, 'user': user,
+            'variation': 1, 'value': 'value', 'default': 'default',
+            'trackEvents': False, 'debugEventsUntilDate': debug_until
+        }
+        ep.send_event(e)
+
+        # Should get a summary event only, not a full feature event
+        output = flush_and_get_events(ep)
+        assert len(output) == 3
+        check_index_event(output[0], e, user)
+        check_feature_event(output[1], e, True, user)  # debug event
+        check_summary_event(output[2])
+
 def test_debug_mode_expires_based_on_client_time_if_client_time_is_later_than_server_time():
     with DefaultTestProcessor() as ep:
         # Pick a server time that is somewhat behind the client time