diff --git a/lib/src/request/async_xhr_request_client.dart b/lib/src/request/async_xhr_request_client.dart
index 8eceda6..72327f2 100644
--- a/lib/src/request/async_xhr_request_client.dart
+++ b/lib/src/request/async_xhr_request_client.dart
@@ -23,9 +23,10 @@
 
     final headers = {
       'Accept': 'application/json',
-      ..._headers,
     };
 
+    headers.addAll(_headers);
+
     HttpRequest httpRequest;
 
     try {
diff --git a/test/async_mouse_test.dart b/test/async_mouse_test.dart
index 0706b32..4f34ed6 100644
--- a/test/async_mouse_test.dart
+++ b/test/async_mouse_test.dart
@@ -15,6 +15,7 @@
 @TestOn('vm')
 library webdriver.mouse_test;
 
+import 'dart:async';
 import 'dart:io';
 
 import 'package:test/test.dart';
diff --git a/test/configs/async_io_config.dart b/test/configs/async_io_config.dart
index ddc7a4a..a20f1fe 100644
--- a/test/configs/async_io_config.dart
+++ b/test/configs/async_io_config.dart
@@ -16,7 +16,6 @@
 import 'dart:io';
 
 import 'package:matcher/matcher.dart';
-import 'package:path/path.dart' as path;
 import 'package:webdriver/async_core.dart'
     show WebDriver, WebDriverSpec, WebElement;
 import 'package:webdriver/async_io.dart' show createDriver;