diff --git a/synapse/crypto/context_factory.py b/synapse/crypto/context_factory.py
index 2b03f5ac7..79668a402 100644
--- a/synapse/crypto/context_factory.py
+++ b/synapse/crypto/context_factory.py
@@ -45,7 +45,11 @@ _TLS_VERSION_MAP = {
 
 class ServerContextFactory(ContextFactory):
     """Factory for PyOpenSSL SSL contexts that are used to handle incoming
-    connections."""
+    connections.
+
+    TODO: replace this with an implementation of IOpenSSLServerConnectionCreator,
+    per https://github.com/matrix-org/synapse/issues/1691
+    """
 
     def __init__(self, config):
         # TODO: once pyOpenSSL exposes TLS_METHOD and SSL_CTX_set_min_proto_version,