diff --git a/ts/lib/generated/post.ts b/ts/lib/generated/post.ts
index d3f44cd09..be9e962be 100644
--- a/ts/lib/generated/post.ts
+++ b/ts/lib/generated/post.ts
@@ -1,13 +1,16 @@
 // Copyright: Ankitects Pty Ltd and contributors
 // License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
+import { isWindows } from "@tslib/platform";
+
 export interface PostProtoOptions {
     /** True by default. Shows a dialog with the error message, then rethrows. */
     alertOnError?: boolean;
+    // whether to use the "anki:" custom protocol or not
     customProtocol?: boolean;
 }
 
-const CUSTOM_PROTOCOL_URI = (navigator.platform.indexOf("Win") == -1) ? "anki://localhost" : "http://anki.localhost";
+const CUSTOM_PROTOCOL_URI = isWindows() ? "http://anki.localhost" : "anki://localhost" ;
 
 export async function postProto<T>(
     method: string,
diff --git a/ts/lib/tslib/platform.ts b/ts/lib/tslib/platform.ts
index d055bcb53..d9727c3a2 100644
--- a/ts/lib/tslib/platform.ts
+++ b/ts/lib/tslib/platform.ts
@@ -10,6 +10,11 @@ export function isApplePlatform(): boolean {
     );
 }
 
+export function isWindows(): boolean {
+    const platform = window.navigator["platform" + ""];
+    return platform.startsWith("Win");
+}
+
 export function isDesktop(): boolean {
     return !(/iphone|ipad|ipod|android/i.test(window.navigator.userAgent));
 }