diff --git a/keyserver/src/responders/message-responders.js b/keyserver/src/responders/message-responders.js
--- a/keyserver/src/responders/message-responders.js
+++ b/keyserver/src/responders/message-responders.js
@@ -481,8 +481,8 @@
 
 const searchMessagesResponderInputValidator = tShape({
   query: t.String,
-  threadID: t.String,
-  cursor: t.maybe(t.String),
+  threadID: tID,
+  cursor: t.maybe(tID),
 });
 
 const searchMessagesResponseValidator: TInterface<SearchMessagesResponse> =