diff --git a/synapse/events/third_party_rules.py b/synapse/events/third_party_rules.py
index 768cfa8e9c6b106954f59ee4cbb2bf263eeffe61..50ceeb1e8ea741d28385390b3fb47293943945eb 100644
--- a/synapse/events/third_party_rules.py
+++ b/synapse/events/third_party_rules.py
@@ -85,6 +85,7 @@ class ThirdPartyEventRules(object):
             requester, config, is_requester_admin
         )
 
+    @defer.inlineCallbacks
     def check_threepid_can_be_invited(self, medium, address, room_id):
         """Check if a provided 3PID can be invited in the given room.