diff --git a/synapse/handlers/read_marker.py b/synapse/handlers/read_marker.py
index 19decc2c6..c3882313e 100644
--- a/synapse/handlers/read_marker.py
+++ b/synapse/handlers/read_marker.py
@@ -42,41 +42,17 @@ class ReadMarkerHandler(BaseHandler):
         """
 
         # Get ordering for existing read marker
-        with (yield self.read_marker_linearizer.queue(room_id + "_" + user_id)):
+        with (yield self.read_marker_linearizer.queue((room_id, user_id))):
             account_data = yield self.store.get_account_data_for_room(user_id, room_id)
             existing_read_marker = account_data["m.read_marker"]
 
             should_update = True
 
-            res = yield self.store._simple_select_one(
-                table="events",
-                retcols=["topological_ordering", "stream_ordering"],
-                keyvalues={"event_id": event_id},
-                allow_none=True
-            )
-
-            if not res:
-                raise SynapseError(404, 'Event does not exist')
-
             if existing_read_marker:
-                new_to = int(res["topological_ordering"])
-                new_so = int(res["stream_ordering"])
-
-                # Get ordering for existing read marker
-                res = yield self.store._simple_select_one(
-                    table="events",
-                    retcols=["topological_ordering", "stream_ordering"],
-                    keyvalues={"event_id": existing_read_marker['marker']},
-                    allow_none=True
+                should_update = yield self.store.is_event_after(
+                    existing_read_marker['marker'],
+                    event_id
                 )
-                existing_to = int(res["topological_ordering"]) if res else None
-                existing_so = int(res["stream_ordering"]) if res else None
-
-                # Prevent updating if the existing marker is ahead in the stream
-                if existing_to > new_to:
-                    should_update = False
-                elif existing_to == new_to and existing_so >= new_so:
-                    should_update = False
 
             if should_update:
                 content = {
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 64fe937bd..3c6df5c2d 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -2159,6 +2159,34 @@ class EventsStore(SQLBaseStore):
             ]
         )
 
+    @defer.inlineCallbacks
+    def is_event_after(self, event_id1, event_id2):
+        is_after = True
+
+        to_1, so_1 = yield self._get_event_ordering(event_id1)
+        to_2, so_2 = yield self._get_event_ordering(event_id2)
+
+        # Prevent updating if the existing marker is ahead in the stream
+        if to_1 > to_2:
+            is_after = False
+        elif to_1 == to_2 and so_1 >= so_2:
+            is_after = False
+
+        defer.returnValue(is_after)
+
+    @defer.inlineCallbacks
+    def _get_event_ordering(self, event_id):
+        res = yield self._simple_select_one(
+            table="events",
+            retcols=["topological_ordering", "stream_ordering"],
+            keyvalues={"event_id": event_id},
+            allow_none=True
+        )
+
+        if not res:
+            raise SynapseError(404, "Could not find event %s" % (event_id,))
+
+        defer.returnValue((int(res["topological_ordering"]), int(res["stream_ordering"])))
 
 AllNewEventsResult = namedtuple("AllNewEventsResult", [
     "new_forward_events", "new_backfill_events",