diff --git a/src/BasePlatform.ts b/src/BasePlatform.ts
index d54dc7dd23..aed063ca32 100644
--- a/src/BasePlatform.ts
+++ b/src/BasePlatform.ts
@@ -227,6 +227,15 @@ export default abstract class BasePlatform {
         return url;
     }
 
+    // persist hs url and is url for when the user is returned to the app with the login token
+    // MUST be called before using URLs from getSSOCallbackUrl, internally called by startSingleSignOn
+    persistSSODetails(mxClient: MatrixClient) {
+        localStorage.setItem(HOMESERVER_URL_KEY, mxClient.getHomeserverUrl());
+        if (mxClient.getIdentityServerUrl()) {
+            localStorage.setItem(ID_SERVER_URL_KEY, mxClient.getIdentityServerUrl());
+        }
+    }
+
     /**
      * Begin Single Sign On flows.
      * @param {MatrixClient} mxClient the matrix client using which we should start the flow
@@ -234,11 +243,7 @@ export default abstract class BasePlatform {
      * @param {string} fragmentAfterLogin the hash to pass to the app during sso callback.
      */
     startSingleSignOn(mxClient: MatrixClient, loginType: "sso" | "cas", fragmentAfterLogin: string) {
-        // persist hs url and is url for when the user is returned to the app with the login token
-        localStorage.setItem(HOMESERVER_URL_KEY, mxClient.getHomeserverUrl());
-        if (mxClient.getIdentityServerUrl()) {
-            localStorage.setItem(ID_SERVER_URL_KEY, mxClient.getIdentityServerUrl());
-        }
+        this.persistSSODetails(mxClient);
         const callbackUrl = this.getSSOCallbackUrl(fragmentAfterLogin);
         window.location.href = mxClient.getSsoLoginUrl(callbackUrl.toString(), loginType); // redirect to SSO
     }
diff --git a/src/components/views/auth/Welcome.js b/src/components/views/auth/Welcome.js
index 91ba368f70..c01b846739 100644
--- a/src/components/views/auth/Welcome.js
+++ b/src/components/views/auth/Welcome.js
@@ -45,8 +45,8 @@ export default class Welcome extends React.PureComponent {
             idBaseUrl: isUrl,
         });
         const plaf = PlatformPeg.get();
-        const callbackUrl = plaf.getSSOCallbackUrl(tmpClient.getHomeserverUrl(), tmpClient.getIdentityServerUrl(),
-            this.props.fragmentAfterLogin);
+        plaf.persistSSODetails(tmpClient);
+        const callbackUrl = plaf.getSSOCallbackUrl(this.props.fragmentAfterLogin);
 
         return (
             <AuthPage>