diff --git a/CHANGELOG.md b/CHANGELOG.md
index 84094d93..d43dea18 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Removed
 
 - **BREAKING**: Deprecated client `Redmine\Client` was removed, use `Redmine\Client\NativeCurlClient` or `Redmine\Client\Psr18Client` instead
+- **BREAKING**: `src/autoload.php` was removed, use the `vendor/autoload.php` from Composer instead
 
 ## [v1.8.1](https://github.com/kbsali/php-redmine-api/compare/v1.8.0...v1.8.1) - 2021-06-01
 
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 86e9e571..f9c81635 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" backupGlobals="false" backupStaticAttributes="false" colors="true" convertErrorsToExceptions="true" convertNoticesToExceptions="true" convertWarningsToExceptions="true" processIsolation="false" stopOnFailure="false" bootstrap="src/autoload.php" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" backupGlobals="false" backupStaticAttributes="false" colors="true" convertErrorsToExceptions="true" convertNoticesToExceptions="true" convertWarningsToExceptions="true" processIsolation="false" stopOnFailure="false" bootstrap="vendor/autoload.php" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
   <coverage>
     <include>
       <directory suffix=".php">src/Redmine/</directory>
diff --git a/src/autoload.php b/src/autoload.php
deleted file mode 100644
index 646ee385..00000000
--- a/src/autoload.php
+++ /dev/null
@@ -1,47 +0,0 @@
-<?php
-
-// use Composer if possible
-$composerPath = __DIR__.'/../vendor/autoload.php';
-
-if (file_exists($composerPath)) {
-    include $composerPath;
-
-    return;
-}
-
-/*
- * PSR-4 implementation for Redmine
- *
- * @param string $class The fully-qualified class name.
- * @return void
- */
-spl_autoload_register(function ($class) {
-    // project-specific namespace prefix and base directory with trailing /
-    $namespaceMap = [
-        'Redmine\\' => __DIR__.'/Redmine/',
-        'Redmine\\Tests\\' => __DIR__.'/../tests/',
-    ];
-
-    foreach ($namespaceMap as $prefix => $baseDir) {
-        // does the class use the namespace prefix?
-        $len = strlen($prefix);
-        if (0 !== strncmp($prefix, $class, $len)) {
-            // no, move to the next registered autoloader
-            continue;
-        }
-
-        // get the relative class name
-        $relativeClass = substr($class, $len);
-
-        // replace the namespace prefix with the base directory, replace namespace
-        // separators with directory separators in the relative class name, append
-        // with .php
-        $file = $baseDir.str_replace('\\', '/', $relativeClass).'.php';
-
-        // if the file exists, require it
-        if (file_exists($file)) {
-            require $file;
-            break;
-        }
-    }
-});