diff --git a/lib/client.js b/lib/client.js
index 139b3b7c6..ff202eca4 100644
--- a/lib/client.js
+++ b/lib/client.js
@@ -2186,7 +2186,8 @@ MatrixClient.prototype.getRoomDirectoryVisibility =
 /**
  * Set the visbility of a room in the current HS's room directory
  * @param {string} roomId
- * @param {string} visibility
+ * @param {string} "public" to make the room visible in the public directory,
+ *                 or "private" to make it invisible.
  * @param {module:client.callback} callback Optional.
  * @return {module:client.Promise} Resolves: result object
  * @return {module:http-api.MatrixError} Rejects: with an error response.