diff --git a/apps/chrome-extension/src/entrypoints/sidepanel/setup-runtime.ts b/apps/chrome-extension/src/entrypoints/sidepanel/setup-runtime.ts
index bab9b9d3..011ff05b 100644
--- a/apps/chrome-extension/src/entrypoints/sidepanel/setup-runtime.ts
+++ b/apps/chrome-extension/src/entrypoints/sidepanel/setup-runtime.ts
@@ -5,7 +5,9 @@ export type PlatformKind = "mac" | "windows" | "linux" | "other";
 
 export function resolvePlatformKind(): PlatformKind {
   const nav = navigator as Navigator & { userAgentData?: { platform?: string } };
-  const raw = (nav.userAgentData?.platform ?? navigator.platform ?? navigator.userAgent ?? "")
+  const uaPlatform = nav.userAgentData?.platform;
+  const effectivePlatform = (uaPlatform && uaPlatform.trim()) ? uaPlatform : navigator.platform;
+  const raw = (effectivePlatform ?? navigator.userAgent ?? "")
     .toLowerCase()
     .trim();