diff --git a/src/AuthHandler/Guzzle6AuthHandler.php b/src/AuthHandler/Guzzle6AuthHandler.php
index 7e8a815c2..0c4d12852 100644
--- a/src/AuthHandler/Guzzle6AuthHandler.php
+++ b/src/AuthHandler/Guzzle6AuthHandler.php
@@ -74,10 +74,18 @@ public function attachToken(ClientInterface $http, array $token, array $scopes)
             return $token['access_token'];
         };
 
+        // Derive a cache prefix from the token, to ensure setting a new token
+        // results in a cache-miss.
+        // Note: Supplying a custom "prefix" will bust this behavior.
+        $cacheConfig = $this->cacheConfig;
+        if (!isset($cacheConfig['prefix']) && isset($token['access_token'])) {
+            $cacheConfig['prefix'] = substr(sha1($token['access_token']), -10);
+        }
+
         $middleware = new ScopedAccessTokenMiddleware(
             $tokenFunc,
             $scopes,
-            $this->cacheConfig,
+            $cacheConfig,
             $this->cache
         );
 
diff --git a/tests/Google/AuthHandler/AuthHandlerTest.php b/tests/Google/AuthHandler/AuthHandlerTest.php
new file mode 100644
index 000000000..0bc34aa82
--- /dev/null
+++ b/tests/Google/AuthHandler/AuthHandlerTest.php
@@ -0,0 +1,82 @@
+<?php
+/**
+ * Copyright 2022 Google LLC
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+namespace Google\Tests\AuthHandler;
+
+use Google\AuthHandler\AuthHandlerFactory;
+use Google\Auth\Cache\MemoryCacheItemPool;
+use GuzzleHttp\Client;
+use GuzzleHttp\Psr7\Request;
+use Google\Tests\BaseTest;
+
+class AuthHandlerTest extends BaseTest
+{
+    public function testSetAccessTokenResultsInAuthCacheMiss()
+    {
+        $client = new Client();
+        $cache = new MemoryCacheItemPool();
+        $authHandler = AuthHandlerFactory::build($cache);
+        $scopes = ['scope1', 'scope2'];
+
+        // Attach the first token to the HTTP client
+        $http1 = $authHandler->attachToken(
+            $client,
+            ['access_token' => '1234'],
+            $scopes
+        );
+
+        // Call our middleware and verify the token is set
+        $scopedMiddleware = $this->getGoogleAuthMiddleware($http1);
+        $request = $scopedMiddleware(new Request('GET', '/'), ['auth' => 'scoped']);
+        $this->assertEquals(['Bearer 1234'], $request->getHeader('Authorization'));
+
+        // Attach a new token to the HTTP client
+        $http2 = $authHandler->attachToken(
+            $client,
+            ['access_token' => '5678'],
+            $scopes
+        );
+
+        // Call our middleware and verify the NEW token is set
+        $scopedMiddleware = $this->getGoogleAuthMiddleware($http2);
+        $request = $scopedMiddleware(new Request('GET', '/'), ['auth' => 'scoped']);
+        $this->assertEquals(['Bearer 5678'], $request->getHeader('Authorization'));
+    }
+
+    private function getGoogleAuthMiddleware(Client $http)
+    {
+        // All sorts of horrible reflection to get at our middleware
+        $handler = $http->getConfig()['handler'];
+        $reflectionMethod = new \ReflectionMethod($handler, 'findByName');
+        $reflectionMethod->setAccessible(true);
+        $authMiddlewareIdx = $reflectionMethod->invoke($handler, 'google_auth');
+
+        $reflectionProperty = new \ReflectionProperty($handler, 'stack');
+        $reflectionProperty->setAccessible(true);
+        $stack = $reflectionProperty->getValue($handler);
+
+        $callable = $stack[$authMiddlewareIdx][0];
+        return $callable(function ($request) {
+            return $request;
+        });
+    }
+}