diff --git a/src/base-apis.js b/src/base-apis.js
index 3e40ee988..68fc137a7 100644
--- a/src/base-apis.js
+++ b/src/base-apis.js
@@ -117,6 +117,15 @@ MatrixBaseApis.prototype.getIdentityServerUrl = function(stripProto=false) {
     return this.idBaseUrl;
 };
 
+/**
+ * Set the Identity Server URL of this client
+ * @param {string} url New Identity Server URL
+ */
+MatrixBaseApis.prototype.setIdentityServerUrl = function(url) {
+    this.idBaseUrl = utils.ensureNoTrailingSlash(url);
+    this._http.setIdBaseUrl(this._idBaseUrl);
+};
+
 /**
  * Get the access token associated with this account.
  * @return {?String} The access_token or null
diff --git a/src/client.js b/src/client.js
index e1367dffa..08cee844b 100644
--- a/src/client.js
+++ b/src/client.js
@@ -161,15 +161,8 @@ function keyFromRecoverySession(session, decryptionKey) {
  * implements the {$link module:crypto/verification/Base verifier interface}.
  */
 function MatrixClient(opts) {
-    // Allow trailing slash in HS url
-    if (opts.baseUrl && opts.baseUrl.endsWith("/")) {
-        opts.baseUrl = opts.baseUrl.substr(0, opts.baseUrl.length - 1);
-    }
-
-    // Allow trailing slash in IS url
-    if (opts.idBaseUrl && opts.idBaseUrl.endsWith("/")) {
-        opts.idBaseUrl = opts.idBaseUrl.substr(0, opts.idBaseUrl.length - 1);
-    }
+    opts.baseUrl = utils.ensureNoTrailingSlash(opts.baseUrl);
+    opts.idBaseUrl = utils.ensureNoTrailingSlash(opts.idBaseUrl);
 
     MatrixBaseApis.call(this, opts);
 
diff --git a/src/http-api.js b/src/http-api.js
index 1f30c23a8..7853ea18f 100644
--- a/src/http-api.js
+++ b/src/http-api.js
@@ -96,6 +96,13 @@ module.exports.MatrixHttpApi = function MatrixHttpApi(event_emitter, opts) {
 };
 
 module.exports.MatrixHttpApi.prototype = {
+    /**
+     * Sets the baase URL for the identity server
+     * @param {string} url The new base url
+     */
+    setIdBaseUrl: function(url) {
+        this.opts.idBaseUrl = url;
+    },
 
     /**
      * Get the content repository url with query parameters.
diff --git a/src/utils.js b/src/utils.js
index d05697f19..b752299f0 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -1,5 +1,6 @@
 /*
 Copyright 2015, 2016 OpenMarket Ltd
+Copyright 2019 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -699,3 +700,11 @@ module.exports.globToRegexp = function(glob, extended) {
     }
     return pat;
 };
+
+module.exports.ensureNoTrailingSlash = function(url) {
+    if (url && url.endsWith("/")) {
+        return url.substr(0, url.length - 1);
+    } else {
+        return url;
+    }
+};