diff --git a/changelog.d/6212.bugfix b/changelog.d/6212.bugfix
new file mode 100644
index 0000000000..918755fee0
--- /dev/null
+++ b/changelog.d/6212.bugfix
@@ -0,0 +1 @@
+Fix bug where presence would not get timed out correctly if a synchrotron worker is used and restarted.
diff --git a/synapse/handlers/presence.py b/synapse/handlers/presence.py
index 2a5f1a007d..eda15bc623 100644
--- a/synapse/handlers/presence.py
+++ b/synapse/handlers/presence.py
@@ -24,6 +24,7 @@ The methods that define policy are:
 
 import logging
 from contextlib import contextmanager
+from typing import Dict, Set
 
 from six import iteritems, itervalues
 
@@ -179,8 +180,9 @@ class PresenceHandler(object):
         # we assume that all the sync requests on that process have stopped.
         # Stored as a dict from process_id to set of user_id, and a dict of
         # process_id to millisecond timestamp last updated.
-        self.external_process_to_current_syncs = {}
-        self.external_process_last_updated_ms = {}
+        self.external_process_to_current_syncs = {}  # type: Dict[int, Set[str]]
+        self.external_process_last_updated_ms = {}  # type: Dict[int, int]
+
         self.external_sync_linearizer = Linearizer(name="external_sync_linearizer")
 
         # Start a LoopingCall in 30s that fires every 5s.
@@ -349,10 +351,13 @@ class PresenceHandler(object):
             if now - last_update > EXTERNAL_PROCESS_EXPIRY
         ]
         for process_id in expired_process_ids:
+            # For each expired process drop tracking info and check the users
+            # that were syncing on that process to see if they need to be timed
+            # out.
             users_to_check.update(
-                self.external_process_last_updated_ms.pop(process_id, ())
+                self.external_process_to_current_syncs.pop(process_id, ())
             )
-            self.external_process_last_update.pop(process_id)
+            self.external_process_last_updated_ms.pop(process_id)
 
         states = [
             self.user_to_current_state.get(user_id, UserPresenceState.default(user_id))
diff --git a/tests/handlers/test_presence.py b/tests/handlers/test_presence.py
index f70c6e7d65..d4293b4312 100644
--- a/tests/handlers/test_presence.py
+++ b/tests/handlers/test_presence.py
@@ -22,6 +22,7 @@ from synapse.api.constants import EventTypes, Membership, PresenceState
 from synapse.events import room_version_to_event_format
 from synapse.events.builder import EventBuilder
 from synapse.handlers.presence import (
+    EXTERNAL_PROCESS_EXPIRY,
     FEDERATION_PING_INTERVAL,
     FEDERATION_TIMEOUT,
     IDLE_TIMER,
@@ -413,6 +414,44 @@ class PresenceTimeoutTestCase(unittest.TestCase):
         self.assertEquals(state, new_state)
 
 
+class PresenceHandlerTestCase(unittest.HomeserverTestCase):
+    def prepare(self, reactor, clock, hs):
+        self.presence_handler = hs.get_presence_handler()
+        self.clock = hs.get_clock()
+
+    def test_external_process_timeout(self):
+        """Test that if an external process doesn't update the records for a while
+        we time out their syncing users presence.
+        """
+        process_id = 1
+        user_id = "@test:server"
+
+        # Notify handler that a user is now syncing.
+        self.get_success(
+            self.presence_handler.update_external_syncs_row(
+                process_id, user_id, True, self.clock.time_msec()
+            )
+        )
+
+        # Check that if we wait a while without telling the handler the user has
+        # stopped syncing that their presence state doesn't get timed out.
+        self.reactor.advance(EXTERNAL_PROCESS_EXPIRY / 2)
+
+        state = self.get_success(
+            self.presence_handler.get_state(UserID.from_string(user_id))
+        )
+        self.assertEqual(state.state, PresenceState.ONLINE)
+
+        # Check that if the external process timeout fires, then the syncing
+        # user gets timed out
+        self.reactor.advance(EXTERNAL_PROCESS_EXPIRY)
+
+        state = self.get_success(
+            self.presence_handler.get_state(UserID.from_string(user_id))
+        )
+        self.assertEqual(state.state, PresenceState.OFFLINE)
+
+
 class PresenceJoinTestCase(unittest.HomeserverTestCase):
     """Tests remote servers get told about presence of users in the room when
     they join and when new local users join.
diff --git a/tox.ini b/tox.ini
index 367cc2ccf2..7ba6f6339f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -161,7 +161,7 @@ basepython = python3.7
 skip_install = True
 deps =
     {[base]deps}
-    mypy
+    mypy==0.730
     mypy-zope
 env =
     MYPYPATH = stubs/