diff --git a/.travis.yml b/.travis.yml
index f3b5e35..34f3c2a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,10 +1,10 @@
 language: php
+dist: trusty
 php:
+  - "7.4"
+  - "7.3"
+  - "7.2"
   - "7.1"
-  - "7.0"
-  - "5.6"
-  - "5.5"
-  - "5.4"
 
 install:
   - sudo apt-get update
diff --git a/composer.json b/composer.json
index f2afa34..2dd69e9 100644
--- a/composer.json
+++ b/composer.json
@@ -1,21 +1,30 @@
 {
-    "name": "codemix/yii2-configloader",
-    "description": "Build configuration arrays from config files and env vars.",
-    "keywords": ["yii2", "config", "environment"],
-    "license": "MIT",
-    "authors": [
-        {
-            "name": "Michael Härtl",
-            "email": "haertl.mike@gmail.com"
-        }
-    ],
-    "require": {
-      "yiisoft/yii2": "*",
-      "vlucas/phpdotenv": "2.5.*"
-    },
-    "autoload": {
-        "psr-4": {
-            "codemix\\yii2confload\\": "src/"
-        }
+  "name": "codemix/yii2-configloader",
+  "description": "Build configuration arrays from config files and env vars.",
+  "keywords": ["yii2", "config", "environment"],
+  "license": "MIT",
+  "authors": [
+    {
+      "name": "Michael Härtl",
+      "email": "haertl.mike@gmail.com"
     }
+  ],
+  "require": {
+    "php": "^7.1.3 || ^8.0",
+    "yiisoft/yii2": "*",
+    "vlucas/phpdotenv": "^5.0"
+  },
+  "require-dev": {
+    "phpunit/phpunit": ">4.0 <8"
+  },
+  "autoload": {
+    "psr-4": {
+      "codemix\\yii2confload\\": "src/"
+    }
+  },
+  "autoload-dev": {
+      "psr-4": {
+          "tests\\": "tests"
+      }
+  }
 }
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 79b8204..a814c26 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -8,7 +8,6 @@
          convertWarningsToExceptions="true"
          processIsolation="true"
          stopOnFailure="false"
-         syntaxCheck="false"
          bootstrap="tests/bootstrap.php"
 >
     <testsuites>
diff --git a/src/Config.php b/src/Config.php
index c2b8ec4..99ea28b 100644
--- a/src/Config.php
+++ b/src/Config.php
@@ -231,7 +231,7 @@ public static function bootstrap($directory, $vendor = null, $initEnv = true)
     public static function initEnv($directory = null)
     {
         if ($directory !== null && file_exists($directory . DIRECTORY_SEPARATOR . '.env')) {
-            $dotenv = new \Dotenv\Dotenv($directory);
+            $dotenv = \Dotenv\Dotenv::createImmutable($directory);
             $dotenv->load();
         }
 
diff --git a/tests/BootstrapTest.php b/tests/BootstrapTest.php
index 8b4ebec..42c21e6 100644
--- a/tests/BootstrapTest.php
+++ b/tests/BootstrapTest.php
@@ -1,7 +1,10 @@
 <?php
+namespace tests;
+
+use \PHPUnit\Framework\TestCase;
 use codemix\yii2confload\Config;
 
-class BootstrapTest extends \PHPUnit\Framework\TestCase
+class BootstrapTest extends TestCase
 {
     public function testCanBootstrapApplication()
     {
diff --git a/tests/ConsoleConfigTest.php b/tests/ConsoleConfigTest.php
index fd2cddd..0ccc1c3 100644
--- a/tests/ConsoleConfigTest.php
+++ b/tests/ConsoleConfigTest.php
@@ -1,7 +1,10 @@
 <?php
+namespace tests;
+
+use \PHPUnit\Framework\TestCase;
 use codemix\yii2confload\Config;
 
-class ConsoleConfigTest extends \PHPUnit\Framework\TestCase
+class ConsoleConfigTest extends TestCase
 {
     public function testCanGetConfig()
     {
diff --git a/tests/EnvTest.php b/tests/EnvTest.php
index 84ee6ed..60d28d4 100644
--- a/tests/EnvTest.php
+++ b/tests/EnvTest.php
@@ -1,7 +1,10 @@
 <?php
+namespace tests;
+
+use \PHPUnit\Framework\TestCase;
 use codemix\yii2confload\Config;
 
-class EnvTest extends \PHPUnit\Framework\TestCase
+class EnvTest extends TestCase
 {
     public function testCanInitYiiEnvFromEnvVars()
     {
@@ -58,11 +61,11 @@ public function testCanGetEnvVarsFromEnvFile()
 
     public function testEnvFileDoesNotClearEnvVars()
     {
-        putenv('TEST1=654');
-        putenv('TEST2=xyz');
+        $_ENV['TEST1'] = '654';
+        $_ENV['TEST2'] = 'xyz';
         Config::initEnv(__DIR__ . '/app');
 
-        $this->assertEquals(654, Config::env('TEST1'));
+        $this->assertEquals('654', Config::env('TEST1'));
         $this->assertEquals('xyz', Config::env('TEST2'));
         $this->assertEquals('dotenv1', Config::env('VAR1'));
         $this->assertEquals(2, Config::env('VAR2'));
@@ -71,13 +74,13 @@ public function testEnvFileDoesNotClearEnvVars()
 
     public function testEnvFileDoesNotOverrideEnvVars()
     {
-        putenv('VAR1=654');
-        putenv('VAR2=xyz');
+        $_ENV['VAR1'] = '654';
+        $_ENV['VAR2'] = 'xyz';
         Config::initEnv(__DIR__ . '/app');
 
         $this->assertEquals(0, Config::env('YII_DEBUG'));
         $this->assertEquals('dev', Config::env('YII_ENV'));
-        $this->assertEquals(654, Config::env('VAR1'));
+        $this->assertEquals('654', Config::env('VAR1'));
         $this->assertEquals('xyz', Config::env('VAR2'));
     }
 
diff --git a/tests/WebConfigTest.php b/tests/WebConfigTest.php
index 75438b4..67b9a49 100644
--- a/tests/WebConfigTest.php
+++ b/tests/WebConfigTest.php
@@ -1,7 +1,10 @@
 <?php
+namespace tests;
+
+use \PHPUnit\Framework\TestCase;
 use codemix\yii2confload\Config;
 
-class WebConfigTest extends \PHPUnit\Framework\TestCase
+class WebConfigTest extends TestCase
 {
     public function testCanGetConfig()
     {