diff --git a/.changeset/lemon-falcons-hunt.md b/.changeset/lemon-falcons-hunt.md
new file mode 100644
index 00000000..3473dabf
--- /dev/null
+++ b/.changeset/lemon-falcons-hunt.md
@@ -0,0 +1,5 @@
+---
+"@openai/agents-core": patch
+---
+
+fix(randomUUID): add fallback when crypto.randomUUID is unavailable
diff --git a/packages/agents-core/src/shims/shims-browser.ts b/packages/agents-core/src/shims/shims-browser.ts
index 231e8c8e..55e5397f 100644
--- a/packages/agents-core/src/shims/shims-browser.ts
+++ b/packages/agents-core/src/shims/shims-browser.ts
@@ -82,7 +82,20 @@ export class BrowserEventEmitter<
 
 export { BrowserEventEmitter as RuntimeEventEmitter };
 
-export const randomUUID = crypto.randomUUID.bind(crypto);
+export const randomUUID: () => `${string}-${string}-${string}-${string}-${string}` =
+  () => {
+    if (typeof crypto !== 'undefined' && crypto.randomUUID) {
+      return crypto.randomUUID();
+    }
+    return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(
+      /[xy]/g,
+      function (c) {
+        const r = (Math.random() * 16) | 0;
+        const v = c === 'x' ? r : (r & 0x3) | 0x8;
+        return v.toString(16);
+      },
+    ) as `${string}-${string}-${string}-${string}-${string}`;
+  };
 export const Readable = class Readable {
   constructor() {}
   pipeTo(
diff --git a/packages/agents-core/test/shims/browser-event-emitter.test.ts b/packages/agents-core/test/shims/browser-event-emitter.test.ts
deleted file mode 100644
index a596366a..00000000
--- a/packages/agents-core/test/shims/browser-event-emitter.test.ts
+++ /dev/null
@@ -1,55 +0,0 @@
-import { describe, expect, test } from 'vitest';
-
-import { BrowserEventEmitter } from '../../src/shims/shims-browser';
-
-describe('BrowserEventEmitter', () => {
-  test('off removes previously registered listener', () => {
-    const emitter = new BrowserEventEmitter<{ foo: [string] }>();
-    const calls: string[] = [];
-
-    const handler = (value: string) => {
-      calls.push(value);
-    };
-
-    emitter.on('foo', handler);
-    emitter.emit('foo', 'first');
-    emitter.off('foo', handler);
-    emitter.emit('foo', 'second');
-
-    expect(calls).toEqual(['first']);
-  });
-
-  test('once triggers listener only once', () => {
-    const emitter = new BrowserEventEmitter<{ foo: [string] }>();
-    let callCount = 0;
-
-    emitter.once('foo', () => {
-      callCount += 1;
-    });
-
-    emitter.emit('foo', 'first');
-    emitter.emit('foo', 'second');
-
-    expect(callCount).toBe(1);
-  });
-
-  test('multiple identical listeners fire for each registration and are removed by off', () => {
-    const emitter = new BrowserEventEmitter<{ foo: [string] }>();
-    const calls: string[] = [];
-
-    const handler = (value: string) => {
-      calls.push(value);
-    };
-
-    emitter.on('foo', handler);
-    emitter.on('foo', handler);
-
-    emitter.emit('foo', 'first');
-    expect(calls).toEqual(['first', 'first']);
-
-    emitter.off('foo', handler);
-    emitter.emit('foo', 'second');
-
-    expect(calls).toEqual(['first', 'first']);
-  });
-});
diff --git a/packages/agents-core/test/shims/browser-shims.test.ts b/packages/agents-core/test/shims/browser-shims.test.ts
new file mode 100644
index 00000000..6fdb6979
--- /dev/null
+++ b/packages/agents-core/test/shims/browser-shims.test.ts
@@ -0,0 +1,120 @@
+import { describe, expect, test, vi } from 'vitest';
+
+import { BrowserEventEmitter, randomUUID } from '../../src/shims/shims-browser';
+
+describe('BrowserEventEmitter', () => {
+  test('off removes previously registered listener', () => {
+    const emitter = new BrowserEventEmitter<{ foo: [string] }>();
+    const calls: string[] = [];
+
+    const handler = (value: string) => {
+      calls.push(value);
+    };
+
+    emitter.on('foo', handler);
+    emitter.emit('foo', 'first');
+    emitter.off('foo', handler);
+    emitter.emit('foo', 'second');
+
+    expect(calls).toEqual(['first']);
+  });
+
+  test('once triggers listener only once', () => {
+    const emitter = new BrowserEventEmitter<{ foo: [string] }>();
+    let callCount = 0;
+
+    emitter.once('foo', () => {
+      callCount += 1;
+    });
+
+    emitter.emit('foo', 'first');
+    emitter.emit('foo', 'second');
+
+    expect(callCount).toBe(1);
+  });
+
+  test('multiple identical listeners fire for each registration and are removed by off', () => {
+    const emitter = new BrowserEventEmitter<{ foo: [string] }>();
+    const calls: string[] = [];
+
+    const handler = (value: string) => {
+      calls.push(value);
+    };
+
+    emitter.on('foo', handler);
+    emitter.on('foo', handler);
+
+    emitter.emit('foo', 'first');
+    expect(calls).toEqual(['first', 'first']);
+
+    emitter.off('foo', handler);
+    emitter.emit('foo', 'second');
+
+    expect(calls).toEqual(['first', 'first']);
+  });
+});
+
+describe('randomUUID', () => {
+  test('uses native crypto.randomUUID when available', () => {
+    const mockUUID = '12345678-1234-1234-1234-123456789abc';
+    const originalCrypto = global.crypto;
+
+    Object.defineProperty(global, 'crypto', {
+      value: { randomUUID: vi.fn(() => mockUUID) },
+      configurable: true,
+    });
+
+    const result = randomUUID();
+    expect(result).toBe(mockUUID);
+    expect(global.crypto.randomUUID).toHaveBeenCalled();
+
+    Object.defineProperty(global, 'crypto', {
+      value: originalCrypto,
+      configurable: true,
+    });
+  });
+
+  test('uses fallback when crypto.randomUUID is unavailable', () => {
+    const originalCrypto = global.crypto;
+
+    Object.defineProperty(global, 'crypto', {
+      value: undefined,
+      configurable: true,
+    });
+
+    const result = randomUUID();
+    expect(result).toMatch(
+      /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/,
+    );
+
+    Object.defineProperty(global, 'crypto', {
+      value: originalCrypto,
+      configurable: true,
+    });
+  });
+
+  test('fallback generates valid UUID v4 format', () => {
+    const originalCrypto = global.crypto;
+
+    Object.defineProperty(global, 'crypto', {
+      value: undefined,
+      configurable: true,
+    });
+
+    const uuids = Array.from({ length: 10 }, () => randomUUID());
+
+    uuids.forEach((uuid) => {
+      expect(uuid).toMatch(
+        /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/,
+      );
+    });
+
+    const uniqueUUIDs = new Set(uuids);
+    expect(uniqueUUIDs.size).toBe(uuids.length);
+
+    Object.defineProperty(global, 'crypto', {
+      value: originalCrypto,
+      configurable: true,
+    });
+  });
+});