diff --git a/lib/base-apis.js b/lib/base-apis.js
index 7a8c62a5c..9e90c3452 100644
--- a/lib/base-apis.js
+++ b/lib/base-apis.js
@@ -715,6 +715,7 @@ MatrixBaseApis.prototype.addThreePid = function(creds, bind, callback) {
 /**
  * @param {string} medium The threepid medium (eg. 'email')
  * @param {string} address The threepid address (eg. 'bob@example.com')
+ *        this must be as returned by getThreePids.
  * @return {module:client.Promise} Resolves: The server response on success
  *     (generally the empty JSON object)
  * @return {module:http-api.MatrixError} Rejects: with an error response.