diff --git a/changelog.d/3616.misc b/changelog.d/3616.misc
new file mode 100644
index 000000000..04629faa3
--- /dev/null
+++ b/changelog.d/3616.misc
@@ -0,0 +1 @@
+Update the /send_leave path registration to use event_id rather than a transaction ID.
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index c9beca27c..8574898f0 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -404,10 +404,10 @@ class FederationMakeLeaveServlet(BaseFederationServlet):
 
 
 class FederationSendLeaveServlet(BaseFederationServlet):
-    PATH = "/send_leave/(?P<room_id>[^/]*)/(?P<txid>[^/]*)"
+    PATH = "/send_leave/(?P<room_id>[^/]*)/(?P<event_id>[^/]*)"
 
     @defer.inlineCallbacks
-    def on_PUT(self, origin, content, query, room_id, txid):
+    def on_PUT(self, origin, content, query, room_id, event_id):
         content = yield self.handler.on_send_leave_request(origin, content)
         defer.returnValue((200, content))