diff --git a/synapse_antispam/mjolnir/ban_list.py b/synapse_antispam/mjolnir/ban_list.py
index 58d317e..8b7e897 100644
--- a/synapse_antispam/mjolnir/ban_list.py
+++ b/synapse_antispam/mjolnir/ban_list.py
@@ -16,6 +16,7 @@
 import logging
 from .list_rule import ListRule, ALL_RULE_TYPES, USER_RULE_TYPES, SERVER_RULE_TYPES, ROOM_RULE_TYPES
 from twisted.internet import defer
+from synapse.logging.context import LoggingContext
 
 logger = logging.getLogger("synapse.contrib." + __name__)
 
@@ -28,45 +29,49 @@ class BanList(object):
         self.room_rules = []
         self.build()
 
-    @defer.inlineCallbacks
-    def build(self, with_event=None):
-        events = yield self.get_relevant_state_events()
-        if with_event is not None:
-            events = [*events, with_event]
-        self.server_rules = []
-        self.user_rules = []
-        self.room_rules = []
-        for event in events:
-            event_type = event.get("type", "")
-            state_key = event.get("state_key", "")
-            content = event.get("content", {})
-            if state_key is None:
-                continue  # Some message event got in here?
-
-            # Skip over events which are replaced by with_event. We do this
-            # to ensure that when we rebuild the list we're using updated rules.
+    def build(with_event=None):
+        @defer.inlineCallbacks
+        def run(self, with_event=None):
+            events = yield self.get_relevant_state_events()
             if with_event is not None:
-                w_event_type = with_event.get("type", "")
-                w_state_key = with_event.get("state_key", "")
-                w_event_id = with_event.event_id
-                event_id = event.event_id
-                if w_event_type == event_type and w_state_key == state_key and w_event_id != event_id:
-                    continue
+                events = [*events, with_event]
+            self.server_rules = []
+            self.user_rules = []
+            self.room_rules = []
+            for event in events:
+                event_type = event.get("type", "")
+                state_key = event.get("state_key", "")
+                content = event.get("content", {})
+                if state_key is None:
+                    continue  # Some message event got in here?
 
-            entity = content.get("entity", None)
-            recommendation = content.get("recommendation", None)
-            reason = content.get("reason", None)
-            if entity is None or recommendation is None or reason is None:
-                continue  # invalid event
+                # Skip over events which are replaced by with_event. We do this
+                # to ensure that when we rebuild the list we're using updated rules.
+                if with_event is not None:
+                    w_event_type = with_event.get("type", "")
+                    w_state_key = with_event.get("state_key", "")
+                    w_event_id = with_event.event_id
+                    event_id = event.event_id
+                    if w_event_type == event_type and w_state_key == state_key and w_event_id != event_id:
+                        continue
 
-            logger.info("Adding rule %s/%s with action %s" % (event_type, entity, recommendation))
-            rule = ListRule(entity=entity, action=recommendation, reason=reason, kind=event_type)
-            if event_type in USER_RULE_TYPES:
-                self.user_rules.append(rule)
-            elif event_type in ROOM_RULE_TYPES:
-                self.room_rules.append(rule)
-            elif event_type in SERVER_RULE_TYPES:
-                self.server_rules.append(rule)
+                entity = content.get("entity", None)
+                recommendation = content.get("recommendation", None)
+                reason = content.get("reason", None)
+                if entity is None or recommendation is None or reason is None:
+                    continue  # invalid event
+
+                logger.info("Adding rule %s/%s with action %s" % (event_type, entity, recommendation))
+                rule = ListRule(entity=entity, action=recommendation, reason=reason, kind=event_type)
+                if event_type in USER_RULE_TYPES:
+                    self.user_rules.append(rule)
+                elif event_type in ROOM_RULE_TYPES:
+                    self.room_rules.append(rule)
+                elif event_type in SERVER_RULE_TYPES:
+                    self.server_rules.append(rule)
+
+        with LoggingContext("mjolnir_ban_list_build"):
+            run(with_event=with_event)
 
     def get_relevant_state_events(self):
         return self.api.get_state_events_in_room(self.room_id, [(t, None) for t in ALL_RULE_TYPES])