diff --git a/lib/client.js b/lib/client.js
index 901a9bf92..b0041b542 100644
--- a/lib/client.js
+++ b/lib/client.js
@@ -1359,16 +1359,13 @@ MatrixClient.prototype.inviteByEmail = function(roomId, email, displayName, call
  * @param {string} address The address for the specified medium.
  * @param {string} displayName The human-readable name to show in the room for
  * this invite. MUST NOT be the address.
- * @param {string} idServer Optional. The identity server URL to use for inviting.
  * @param {module:client.callback} callback Optional.
  * @return {module:client.Promise} Resolves: TODO
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  * @throws If <code>displayName</code> contains the <code>address</code>.
  */
 MatrixClient.prototype.inviteByThreePid = function(roomId, medium, address,
-                                                   displayName, idServer, callback) {
-    if (utils.isFunction(idServer)) { callback = idServer; idServer = undefined; }
-    idServer = idServer || this.getIdentityServerUrl();
+                                                   displayName, callback) {
     if (displayName && displayName.indexOf(address) >= 0) {
         throw new Error(
             "The display name contains the address. This leaks the 3PID " +
@@ -1382,7 +1379,7 @@ MatrixClient.prototype.inviteByThreePid = function(roomId, medium, address,
     );
 
     return this._http.authedRequest(callback, "POST", path, undefined, {
-        id_server: idServer,
+        id_server: this.getIdentityServerUrl(),
         medium: medium,
         address: address,
         display_name: displayName