diff --git a/src/Utility/HttpRequest.php b/src/Utility/HttpRequest.php
index 6c3584ee..94ffae1d 100644
--- a/src/Utility/HttpRequest.php
+++ b/src/Utility/HttpRequest.php
@@ -227,7 +227,7 @@ public function call(): ResponseInterface
 
             // Used for unit testing: if we're mocking responses and have a callback assigned, invoke that callback with our request and response.
             // @codeCoverageIgnoreStart
-            if ($mockedResponse && method_exists($mockedResponse, 'callback') && is_callable($mockedResponse->callback)) { // @phpstan-ignore-line
+            if ($mockedResponse && property_exists($mockedResponse, 'callback') && is_callable($mockedResponse->callback)) { // @phpstan-ignore-line
                 ($mockedResponse->callback)($httpRequest, $httpResponse);
             }
             // @codeCoverageIgnoreEnd
diff --git a/tests/Unit/Utility/HttpClientTest.php b/tests/Unit/Utility/HttpClientTest.php
index 127329b1..4b25fbf9 100644
--- a/tests/Unit/Utility/HttpClientTest.php
+++ b/tests/Unit/Utility/HttpClientTest.php
@@ -51,7 +51,7 @@
     }
 
     $response = $this->client->method('get')
-    ->addPath(['client'])
+        ->addPath(['client'])
         ->call();
 
     expect(HttpResponse::getStatusCode($response))->toEqual(429);
@@ -75,7 +75,7 @@
     }
 
     $response = $this->client->method('get')
-    ->addPath(['client'])
+        ->addPath(['client'])
         ->call();
 
     $requestCount = $this->client->getLastRequest()->getRequestCount();
@@ -142,7 +142,7 @@
     $this->client->mockResponse(clone $this->httpResponse200);
 
     $response = $this->client->method('get')
-    ->addPath(['client'])
+        ->addPath(['client'])
         ->call();
 
     expect(HttpResponse::getStatusCode($response))->toEqual(429);
@@ -160,7 +160,7 @@
     ]);
 
     $response = $this->client->method('get')
-    ->addPath(['client'])
+        ->addPath(['client'])
         ->call();
 
     expect(HttpResponse::getStatusCode($response))->toEqual(200);
@@ -169,3 +169,20 @@
 
     expect($requestCount)->toEqual(2);
 });
+
+test('the callback of a mock response is called', function(): void {
+    $count = 0;
+
+    $this->client->mockResponse(
+        clone $this->httpResponse200,
+        function ($request) use (&$count) {
+            $count++;
+        }
+    );
+
+    $response = $this->client->method('get')
+        ->addPath(['client'])
+        ->call();
+
+    expect($count)->toEqual(1);
+});