diff --git a/src/Illuminate/Http/Client/PendingRequest.php b/src/Illuminate/Http/Client/PendingRequest.php
index c3c7e2c39624..854cab79dc20 100644
--- a/src/Illuminate/Http/Client/PendingRequest.php
+++ b/src/Illuminate/Http/Client/PendingRequest.php
@@ -888,7 +888,7 @@ public function delete(string $url, $data = [])
      * @param  int|null  $concurrency
      * @return array<array-key, \Illuminate\Http\Client\Response|\Illuminate\Http\Client\ConnectionException|\Illuminate\Http\Client\RequestException>
      */
-    public function pool(callable $callback, ?int $concurrency = null)
+    public function pool(callable $callback, ?int $concurrency = 0)
     {
         $results = [];
 
diff --git a/tests/Http/HttpClientTest.php b/tests/Http/HttpClientTest.php
index febc488c3a91..aac1afb564cf 100644
--- a/tests/Http/HttpClientTest.php
+++ b/tests/Http/HttpClientTest.php
@@ -3527,14 +3527,14 @@ public function testItCanEnforceFakingInThePool()
         $this->assertSame(200, $responses[0]->status());
         $this->assertSame(200, $responses[1]->status());
 
-        $this->expectException(StrayRequestException::class);
-        $this->expectExceptionMessage('Attempted request to [https://laravel.com] without a matching fake.');
-
-        $this->factory->pool(function (Pool $pool) {
+        [$exception] = $this->factory->pool(function (Pool $pool) {
             return [
                 $pool->get('https://laravel.com'),
             ];
         });
+
+        $this->assertInstanceOf(StrayRequestException::class, $exception);
+        $this->assertEquals('Attempted request to [https://laravel.com] without a matching fake.', $exception->getMessage());
     }
 
     public function testPreventingStrayRequests()