diff --git a/packages/sdk-js/src/network/wsClient.test.ts b/packages/sdk-js/src/network/wsClient.test.ts
index 258dd39..f86f5a7 100644
--- a/packages/sdk-js/src/network/wsClient.test.ts
+++ b/packages/sdk-js/src/network/wsClient.test.ts
@@ -736,4 +736,58 @@ describe('WebSocketClient + WebSocketSession', () => {
 
     expect(limitCloseSpy).toHaveBeenCalledWith({ code: 1002, reason: 'Test close' })
   })
+
+  it('should sanitize reserved close codes in browser environments', async () => {
+    const originalWindow = globalThis.window
+    const originalDocument = globalThis.document
+
+    vi.stubGlobal('window', {})
+    vi.stubGlobal('document', {})
+
+    try {
+      const closeSpy = vi.fn()
+      client = new WebSocketClient(partialOptions())
+      session = client.createSession('ws://localhost:8080')
+      session.onclose = closeSpy
+      await tick()
+      simulateOpen()
+
+      session.close(1001, 'Aborted')
+      expect(mockWs.close).toHaveBeenCalledWith(1000)
+      expect(mockWs.close).not.toHaveBeenCalledWith(1001)
+
+      simulateClose(1000, '')
+      expect(closeSpy).toHaveBeenCalledWith({ code: 1001, reason: 'Aborted' })
+    } finally {
+      vi.stubGlobal('window', originalWindow)
+      vi.stubGlobal('document', originalDocument)
+    }
+  })
+
+  it('should fall back to 1000 when browser close throws InvalidAccessError', async () => {
+    const originalWindow = globalThis.window
+    const originalDocument = globalThis.document
+
+    vi.stubGlobal('window', {})
+    vi.stubGlobal('document', {})
+
+    mockWs.close = vi.fn((code: number) => {
+      if (code !== 1000) {
+        throw new DOMException('Invalid close code', 'InvalidAccessError')
+      }
+    })
+
+    try {
+      client = new WebSocketClient(partialOptions())
+      session = client.createSession('ws://localhost:8080')
+      await tick()
+      simulateOpen()
+
+      expect(() => session.close(1006, 'WebSocket connection error')).not.toThrow()
+      expect(mockWs.close).toHaveBeenLastCalledWith(1000)
+    } finally {
+      vi.stubGlobal('window', originalWindow)
+      vi.stubGlobal('document', originalDocument)
+    }
+  })
 })
diff --git a/packages/sdk-js/src/network/wsClient.ts b/packages/sdk-js/src/network/wsClient.ts
index 436d08b..98759e6 100644
--- a/packages/sdk-js/src/network/wsClient.ts
+++ b/packages/sdk-js/src/network/wsClient.ts
@@ -33,6 +33,35 @@ function removeWsListeners(ws?: IsoWS | null): void {
   ws.onclose = null
 }
 
+/** Browser WebSocket.close() only accepts 1000 or 3000–4999. */
+function isBrowserWebSocketEnvironment(): boolean {
+  const env = globalThis as typeof globalThis & {
+    window?: unknown
+    document?: unknown
+  }
+  return env.window !== undefined && env.document !== undefined
+}
+
+function sanitizeCloseCodeForBrowser(code: number): number {
+  if (code === 1000 || (code >= 3000 && code <= 4999)) {
+    return code
+  }
+  return 1000
+}
+
+function safeWsClose(ws: IsoWS, code: number): void {
+  const closeCode = isBrowserWebSocketEnvironment() ? sanitizeCloseCodeForBrowser(code) : code
+  try {
+    ws.close(closeCode)
+  } catch {
+    try {
+      ws.close(1000)
+    } catch {
+      // ignore
+    }
+  }
+}
+
 export class WebSocketClient {
   private readonly baseUrl: string | URL
   private readonly retry: Required<WebSocketRetryOptions>
@@ -77,6 +106,7 @@ class WebSocketSession implements Omit<IsoWS, 'onopen'> {
   private connectionCount = 0
   private connectionAttempt = 0
   private connectionTimeoutId: ReturnType<typeof setTimeout> | undefined
+  private pendingClose: { code: number; reason: string } | null = null
 
   constructor({
     retry,
@@ -123,9 +153,10 @@ class WebSocketSession implements Omit<IsoWS, 'onopen'> {
 
     this.clearConnectionTimeout()
     this._readyState = WS_STATES.CLOSING
+    this.pendingClose = { code, reason }
 
     if (this.ws?.readyState === WS_STATES.OPEN) {
-      this.ws.close(code)
+      safeWsClose(this.ws, code)
     } /* if (this.readyState === WS_STATES.CONNECTING) */ else {
       this.onWsClose(code, reason)
     }
@@ -147,6 +178,7 @@ class WebSocketSession implements Omit<IsoWS, 'onopen'> {
 
     removeWsListeners(this.ws)
     this.ws = null
+    this.pendingClose = null
   }
 
   private async connect(isRetry = false): Promise<void> {
@@ -198,7 +230,7 @@ class WebSocketSession implements Omit<IsoWS, 'onopen'> {
     }
 
     if (this.readyState !== WS_STATES.CONNECTING) {
-      ws.close(1001)
+      safeWsClose(ws, 1001)
       return
     }
 
@@ -209,7 +241,7 @@ class WebSocketSession implements Omit<IsoWS, 'onopen'> {
 
       if (this.readyState !== WS_STATES.CONNECTING) {
         // User closed the connection during the connection attempt
-        ws.close(1001)
+        safeWsClose(ws, 1001)
         return
       }
 
@@ -227,7 +259,8 @@ class WebSocketSession implements Omit<IsoWS, 'onopen'> {
         this.ws = null
 
         if (this.readyState === WS_STATES.CLOSING) {
-          this.onWsClose(event.code, event.reason || '')
+          const pending = this.pendingClose
+          this.onWsClose(pending?.code ?? event.code, pending?.reason || event.reason || '')
           return
         }
 
diff --git a/packages/sdk-js/src/v2/live/session.test.ts b/packages/sdk-js/src/v2/live/session.test.ts
index f122ad3..5bf4fb5 100644
--- a/packages/sdk-js/src/v2/live/session.test.ts
+++ b/packages/sdk-js/src/v2/live/session.test.ts
@@ -146,4 +146,30 @@ describe('LiveV2Session connectSession', () => {
     })
     expect(session.sessionId).toBe('created-session-id')
   })
+
+  it('endSession does not throw when abort closes the websocket with a reserved code', async () => {
+    const existingSession = {
+      id: 'session-123',
+      url: 'wss://api.gladia.io/v2/live/ws?token=abc',
+      created_at: '2026-06-25T10:00:00Z',
+    }
+
+    mockWsSession.readyState = WS_STATES.OPEN
+    mockWsSession.close = vi.fn(() => {
+      throw new DOMException('Invalid close code', 'InvalidAccessError')
+    })
+
+    const session = new LiveV2Session({
+      options: {},
+      existingSession,
+      httpClient,
+      webSocketClient,
+    })
+
+    await tick()
+    mockWsSession.onopen?.({ connection: 1, attempt: 1 })
+
+    expect(() => session.endSession()).not.toThrow()
+    expect(session.status).toBe('ended')
+  })
 })
diff --git a/packages/sdk-js/src/v2/live/session.ts b/packages/sdk-js/src/v2/live/session.ts
index 9004fed..246b074 100644
--- a/packages/sdk-js/src/v2/live/session.ts
+++ b/packages/sdk-js/src/v2/live/session.ts
@@ -199,7 +199,11 @@ export class LiveV2Session {
       webSocketSession.onmessage = null
       webSocketSession.onclose = null
       webSocketSession.onerror = null
-      webSocketSession.close(1001, 'Aborted')
+      try {
+        webSocketSession.close(1001, 'Aborted')
+      } catch {
+        // Abort listeners route exceptions to window.onerror; swallow close failures.
+      }
     })
 
     this.webSocketSession = webSocketSession