diff --git a/synapse/http/proxyagent.py b/synapse/http/proxyagent.py
index 1fa3adbef20c..fd418fc22512 100644
--- a/synapse/http/proxyagent.py
+++ b/synapse/http/proxyagent.py
@@ -152,7 +152,7 @@ def __init__(
 
                 if federation_proxy.tls:
                     tls_connection_creator = self._policy_for_https.creatorForNetloc(
-                        federation_proxy.host,
+                        federation_proxy.host.encode("utf-8"),
                         federation_proxy.port,
                     )
                     endpoint = wrapClientTLS(tls_connection_creator, endpoint)