diff --git a/synapse/replication/tcp/protocol.py b/synapse/replication/tcp/protocol.py
index 995b47a1eddf..db78b4f4bb04 100644
--- a/synapse/replication/tcp/protocol.py
+++ b/synapse/replication/tcp/protocol.py
@@ -130,7 +130,7 @@ class BaseReplicationStreamProtocol(LineOnlyReceiver):
 
     max_line_buffer = 10000
 
-    def __init__(self, clock, handler):
+    def __init__(self, clock: Clock, handler: "ReplicationCommandHandler"):
         self.clock = clock
         self.handler = handler
 
@@ -420,7 +420,9 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
     VALID_INBOUND_COMMANDS = VALID_CLIENT_COMMANDS
     VALID_OUTBOUND_COMMANDS = VALID_SERVER_COMMANDS
 
-    def __init__(self, server_name, clock, handler):
+    def __init__(
+        self, server_name: str, clock: Clock, handler: "ReplicationCommandHandler"
+    ):
         BaseReplicationStreamProtocol.__init__(self, clock, handler)  # Old style class
 
         self.server_name = server_name