diff --git a/web/src/lib/browser.ts b/web/src/lib/browser.ts
index 8f1f012..6ca04ca 100644
--- a/web/src/lib/browser.ts
+++ b/web/src/lib/browser.ts
@@ -1,28 +1,33 @@
+export type System = 'Windows' | 'macOS' | 'Linux' | 'Unknown';
+
 export interface BrowserInfo {
-  os: string;
+  os: System;
   isChrome: boolean;
 }
 
-export function getOperatingSystem(): string {
+export function getOperatingSystem(): System {
   if (typeof window === 'undefined') {
     return 'Unknown';
   }
 
-  const platformSource =
+  if ('userAgentData' in navigator) {
     // @ts-expect-error check userAgentData.platform
-    'userAgentData' in navigator ? navigator.userAgentData.platform : navigator.platform;
-
-  if (!platformSource) {
-    return 'Unknown';
+    const platform = navigator.userAgentData?.platform?.toLowerCase();
+    if (platform) {
+      if (platform === 'windows') return 'Windows';
+      if (platform === 'macos') return 'macOS';
+      if (platform === 'linux' || platform === 'android') return 'Linux';
+    }
   }
 
-  const platform = platformSource.toLowerCase();
+  // Fallback to User Agent
+  const userAgent = navigator.userAgent;
 
-  if (platform.startsWith('win')) return 'Windows';
-  if (platform.startsWith('mac')) return 'macOS';
-  if (platform.startsWith('linux')) return 'Linux';
+  if (/Win/i.test(userAgent)) return 'Windows';
+  if (/Mac|iPhone|iPod|iPad/i.test(userAgent)) return 'macOS';
+  if (/Linux|Android/i.test(userAgent)) return 'Linux';
 
-  return platformSource;
+  return 'Unknown';
 }
 
 export function isChromeBrowser(): boolean {
diff --git a/web/src/pages/desktop/keyboard/index.tsx b/web/src/pages/desktop/keyboard/index.tsx
index 6514233..8533f3d 100644
--- a/web/src/pages/desktop/keyboard/index.tsx
+++ b/web/src/pages/desktop/keyboard/index.tsx
@@ -7,6 +7,8 @@ import { isModifier } from '@/lib/keymap';
 import { client, MessageEvent } from '@/lib/websocket.ts';
 import { isKeyboardEnableAtom } from '@/jotai/keyboard.ts';
 
+import { normalizeKeyCode } from './utils.ts';
+
 interface AltGrState {
   active: boolean;
   ctrlLeftTimestamp: number;
@@ -23,7 +25,8 @@ export const Keyboard = () => {
   const isComposing = useRef(false);
 
   useEffect(() => {
-    if (getOperatingSystem() === 'Windows' && !altGrState.current) {
+    const os = getOperatingSystem();
+    if (os === 'Windows' && !altGrState.current) {
       altGrState.current = { active: false, ctrlLeftTimestamp: 0 };
     }
 
@@ -49,8 +52,10 @@ export const Keyboard = () => {
       event.preventDefault();
       event.stopPropagation();
 
-      const code = event.code;
-      if (pressedKeys.current.has(code)) return;
+      const code = normalizeKeyCode(event, os);
+      if (!code || pressedKeys.current.has(code)) {
+        return;
+      }
 
       // When AltGr is pressed, browsers send ControlLeft followed immediately by AltRight
       if (altGrState.current) {
@@ -79,7 +84,10 @@ export const Keyboard = () => {
       event.preventDefault();
       event.stopPropagation();
 
-      const code = event.code;
+      const code = normalizeKeyCode(event, os);
+      if (!code) {
+        return;
+      }
 
       // Handle AltGr state for Windows
       if (altGrState.current?.active) {
diff --git a/web/src/pages/desktop/keyboard/utils.ts b/web/src/pages/desktop/keyboard/utils.ts
new file mode 100644
index 0000000..0b199fb
--- /dev/null
+++ b/web/src/pages/desktop/keyboard/utils.ts
@@ -0,0 +1,26 @@
+export function normalizeKeyCode(event: KeyboardEvent, os?: string): string {
+  if (event.code) {
+    return event.code;
+  }
+
+  // Fallback: use event.key + event.location to determine the key
+  // event.location: 1 = left, 2 = right, 0 = standard (non-positional)
+  if (event.key === 'Shift') {
+    if (event.location === 0 && os === 'Windows') {
+      return 'ShiftRight';
+    }
+    return event.location === 2 ? 'ShiftRight' : 'ShiftLeft';
+  }
+
+  if (event.key === 'Control') {
+    return event.location === 2 ? 'ControlRight' : 'ControlLeft';
+  }
+  if (event.key === 'Alt') {
+    return event.location === 2 ? 'AltRight' : 'AltLeft';
+  }
+  if (event.key === 'Meta') {
+    return event.location === 2 ? 'MetaRight' : 'MetaLeft';
+  }
+
+  return event.code;
+}