diff --git a/synapse/crypto/keyring.py b/synapse/crypto/keyring.py
index a16188a01946..4cda439ad927 100644
--- a/synapse/crypto/keyring.py
+++ b/synapse/crypto/keyring.py
@@ -270,7 +270,7 @@ async def process_request(self, verify_request: VerifyJsonRequest) -> None:
                 Codes.UNAUTHORIZED,
             )
 
-        found_keys: Dict[str:FetchKeyResult] = {}
+        found_keys: Dict[str, FetchKeyResult] = {}
 
         # If we are the originating server, short-circuit the key-fetch for any keys
         # we already have