diff --git a/src/__tests__/endpoint.test.ts b/src/__tests__/endpoint.test.ts
index d9aec25a..52fa0943 100644
--- a/src/__tests__/endpoint.test.ts
+++ b/src/__tests__/endpoint.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, mock, test } from 'bun:test';
-import { executeEndpointFallback } from '../endpoint';
+import { executeEndpointFallback, pickRandomEndpoint } from '../endpoint';
 
 const delay = (ms: number) =>
   new Promise<void>(resolve => {
@@ -90,3 +90,34 @@ describe('executeEndpointFallback', () => {
     expect(tryEndpoint.mock.calls.map(call => call[0])).toEqual(['a', 'b', 'c']);
   });
 });
+
+describe('pickRandomEndpoint', () => {
+  test('returns undefined for empty arrays', () => {
+    expect(pickRandomEndpoint([])).toBeUndefined();
+  });
+
+  test('deterministically selects an endpoint using a custom random parameter', () => {
+    const endpoints = ['a', 'b', 'c'];
+
+    // Test random = 0 (picks first)
+    const endpoints1 = [...endpoints];
+    expect(pickRandomEndpoint(endpoints1, () => 0)).toBe('a');
+
+    // Test random = 0.5 (picks middle)
+    const endpoints2 = [...endpoints];
+    expect(pickRandomEndpoint(endpoints2, () => 0.5)).toBe('b');
+
+    // Test random = 0.99 (picks last)
+    const endpoints3 = [...endpoints];
+    expect(pickRandomEndpoint(endpoints3, () => 0.99)).toBe('c');
+  });
+
+  test('mutates the original array by removing the selected endpoint', () => {
+    const endpoints = ['a', 'b', 'c'];
+    const result = pickRandomEndpoint(endpoints, () => 0.5);
+
+    expect(result).toBe('b');
+    expect(endpoints).toEqual(['a', 'c']);
+    expect(endpoints.length).toBe(2);
+  });
+});
diff --git a/src/endpoint.ts b/src/endpoint.ts
index 0c4fb86f..67cbbac6 100644
--- a/src/endpoint.ts
+++ b/src/endpoint.ts
@@ -44,12 +44,11 @@ export const dedupeEndpoints = (
 
 export const pickRandomEndpoint = (
   endpoints: string[],
-  random: () => number = Math.random,
-) => {
-  if (!endpoints.length) {
-    throw new Error('No endpoints configured');
-  }
-  return endpoints[Math.floor(random() * endpoints.length)];
+  random = Math.random,
+): string | undefined => {
+  if (endpoints.length === 0) return undefined;
+  const index = Math.floor(random() * endpoints.length);
+  return endpoints.splice(index, 1)[0];
 };
 
 export async function selectFastestSuccessfulEndpoint<T>(
@@ -124,6 +123,9 @@ export async function executeEndpointFallback<T>({
   }
 
   const firstEndpoint = pickRandomEndpoint(candidates, random);
+  if (!firstEndpoint) {
+    throw new Error('No endpoints configured');
+  }
 
   try {
     return {