diff --git a/src/Container.php b/src/Container.php
index 23175ba..2058379 100644
--- a/src/Container.php
+++ b/src/Container.php
@@ -13,6 +13,9 @@ class Container
     /** @var array<string,object|callable():(object|scalar|null)|scalar|null>|ContainerInterface */
     private $container;
 
+    /** @var bool */
+    private $useProcessEnv;
+
     /** @param array<string,callable():(object|scalar|null) | object | scalar | null>|ContainerInterface $loader */
     public function __construct($loader = [])
     {
@@ -32,6 +35,9 @@ public function __construct($loader = [])
             }
         }
         $this->container = $loader;
+
+        // prefer reading environment from `$_ENV` and `$_SERVER`, only fall back to `getenv()` in thread-safe environments
+        $this->useProcessEnv = \ZEND_THREAD_SAFE === false || \in_array(\PHP_SAPI, ['cli', 'cli-server', 'cgi-fcgi', 'fpm-fcgi'], true);
     }
 
     /** @return mixed */
@@ -98,12 +104,12 @@ public function getEnv(string $name): ?string
     {
         assert(\preg_match('/^[A-Z][A-Z0-9_]+$/', $name) === 1);
 
-        if (\is_array($this->container) && \array_key_exists($name, $this->container)) {
-            $value = $this->loadVariable($name, 'mixed', true, 64);
-        } elseif ($this->container instanceof ContainerInterface && $this->container->has($name)) {
+        if ($this->container instanceof ContainerInterface && $this->container->has($name)) {
             $value = $this->container->get($name);
+        } elseif ($this->hasVariable($name)) {
+            $value = $this->loadVariable($name, 'mixed', true, 64);
         } else {
-            $value = $_SERVER[$name] ?? null;
+            return null;
         }
 
         if (!\is_string($value) && $value !== null) {
@@ -257,7 +263,7 @@ private function loadParameter(\ReflectionParameter $parameter, int $depth, bool
 
         // load container variables if parameter name is known
         assert($type === null || $type instanceof \ReflectionNamedType);
-        if ($allowVariables && (\array_key_exists($parameter->getName(), $this->container) || (isset($_SERVER[$parameter->getName()]) && \preg_match('/^[A-Z][A-Z0-9_]+$/', $parameter->getName())))) {
+        if ($allowVariables && $this->hasVariable($parameter->getName())) {
             return $this->loadVariable($parameter->getName(), $type === null ? 'mixed' : $type->getName(), $parameter->allowsNull(), $depth);
         }
 
@@ -294,15 +300,21 @@ private function loadParameter(\ReflectionParameter $parameter, int $depth, bool
         return $this->loadObject($type->getName(), $depth - 1);
     }
 
+    private function hasVariable(string $name): bool
+    {
+        return (\is_array($this->container) && \array_key_exists($name, $this->container)) || (isset($_ENV[$name]) || (\is_string($_SERVER[$name] ?? null) || ($this->useProcessEnv && \getenv($name) !== false)) && \preg_match('/^[A-Z][A-Z0-9_]+$/', $name));
+    }
+
     /**
      * @return object|string|int|float|bool|null
      * @throws \BadMethodCallException if $name is not a valid container variable
      */
     private function loadVariable(string $name, string $type, bool $nullable, int $depth) /*: object|string|int|float|bool|null (PHP 8.0+) */
     {
-        assert(\is_array($this->container) && (\array_key_exists($name, $this->container) || isset($_SERVER[$name])));
+        assert($this->hasVariable($name));
+        assert(\is_array($this->container) || !$this->container->has($name));
 
-        if (($this->container[$name] ?? null) instanceof \Closure) {
+        if (\is_array($this->container) && ($this->container[$name] ?? null) instanceof \Closure) {
             if ($depth < 1) {
                 throw new \BadMethodCallException('Container variable $' . $name . ' is recursive');
             }
@@ -321,11 +333,17 @@ private function loadVariable(string $name, string $type, bool $nullable, int $d
             }
 
             $this->container[$name] = $value;
-        } elseif (\array_key_exists($name, $this->container)) {
+        } elseif (\is_array($this->container) && \array_key_exists($name, $this->container)) {
             $value = $this->container[$name];
-        } else {
-            assert(isset($_SERVER[$name]) && \is_string($_SERVER[$name]));
+        } elseif (isset($_ENV[$name])) {
+            assert(\is_string($_ENV[$name]));
+            $value = $_ENV[$name];
+        } elseif (isset($_SERVER[$name])) {
+            assert(\is_string($_SERVER[$name]));
             $value = $_SERVER[$name];
+        } else {
+            $value = \getenv($name);
+            assert($this->useProcessEnv && $value !== false);
         }
 
         assert(\is_object($value) || \is_scalar($value) || $value === null);
diff --git a/tests/ContainerTest.php b/tests/ContainerTest.php
index 26423a4..389757c 100644
--- a/tests/ContainerTest.php
+++ b/tests/ContainerTest.php
@@ -2039,6 +2039,17 @@ public function testGetEnvReturnsStringFromMapFactory(): void
         $this->assertEquals('bar', $container->getEnv('X_FOO'));
     }
 
+    public function testGetEnvReturnsStringFromGlobalEnvIfNotSetInMap(): void
+    {
+        $container = new Container([]);
+
+        $_ENV['X_FOO'] = 'bar';
+        $ret = $container->getEnv('X_FOO');
+        unset($_ENV['X_FOO']);
+
+        $this->assertEquals('bar', $ret);
+    }
+
     public function testGetEnvReturnsStringFromGlobalServerIfNotSetInMap(): void
     {
         $container = new Container([]);
@@ -2050,6 +2061,42 @@ public function testGetEnvReturnsStringFromGlobalServerIfNotSetInMap(): void
         $this->assertEquals('bar', $ret);
     }
 
+    public function testGetEnvReturnsStringFromProcessEnvIfNotSetInMap(): void
+    {
+        $container = new Container([]);
+
+        putenv('X_FOO=bar');
+        $ret = $container->getEnv('X_FOO');
+        putenv('X_FOO');
+
+        $this->assertEquals('bar', $ret);
+    }
+
+    public function testGetEnvReturnsStringFromGlobalEnvBeforeServerIfNotSetInMap(): void
+    {
+        $container = new Container([]);
+
+        $_ENV['X_FOO'] = 'foo';
+        $_SERVER['X_FOO'] = 'bar';
+        $ret = $container->getEnv('X_FOO');
+        unset($_ENV['X_FOO'], $_SERVER['X_FOO']);
+
+        $this->assertEquals('foo', $ret);
+    }
+
+    public function testGetEnvReturnsStringFromGlobalEnvBeforeProcessEnvIfNotSetInMap(): void
+    {
+        $container = new Container([]);
+
+        $_ENV['X_FOO'] = 'foo';
+        putenv('X_FOO=bar');
+        $ret = $container->getEnv('X_FOO');
+        unset($_ENV['X_FOO']);
+        putenv('X_FOO');
+
+        $this->assertEquals('foo', $ret);
+    }
+
     public function testGetEnvReturnsStringFromPsrContainer(): void
     {
         $psr = $this->createMock(ContainerInterface::class);
@@ -2074,10 +2121,42 @@ public function testGetEnvReturnsNullIfPsrContainerHasNoEntry(): void
         $this->assertNull($container->getEnv('X_FOO'));
     }
 
+    public function testGetEnvReturnsStringFromProcessEnvIfPsrContainerHasNoEntry(): void
+    {
+        $psr = $this->createMock(ContainerInterface::class);
+        $psr->expects($this->atLeastOnce())->method('has')->with('X_FOO')->willReturn(false);
+        $psr->expects($this->never())->method('get');
+
+        assert($psr instanceof ContainerInterface);
+        $container = new Container($psr);
+
+        putenv('X_FOO=bar');
+        $ret = $container->getEnv('X_FOO');
+        putenv('X_FOO');
+
+        $this->assertEquals('bar', $ret);
+    }
+
+    public function testGetEnvReturnsStringFromGlobalEnvIfPsrContainerHasNoEntry(): void
+    {
+        $psr = $this->createMock(ContainerInterface::class);
+        $psr->expects($this->atLeastOnce())->method('has')->with('X_FOO')->willReturn(false);
+        $psr->expects($this->never())->method('get');
+
+        assert($psr instanceof ContainerInterface);
+        $container = new Container($psr);
+
+        $_ENV['X_FOO'] = 'bar';
+        $ret = $container->getEnv('X_FOO');
+        unset($_ENV['X_FOO']);
+
+        $this->assertEquals('bar', $ret);
+    }
+
     public function testGetEnvReturnsStringFromGlobalServerIfPsrContainerHasNoEntry(): void
     {
         $psr = $this->createMock(ContainerInterface::class);
-        $psr->expects($this->once())->method('has')->with('X_FOO')->willReturn(false);
+        $psr->expects($this->atLeastOnce())->method('has')->with('X_FOO')->willReturn(false);
         $psr->expects($this->never())->method('get');
 
         assert($psr instanceof ContainerInterface);
@@ -2090,6 +2169,41 @@ public function testGetEnvReturnsStringFromGlobalServerIfPsrContainerHasNoEntry(
         $this->assertEquals('bar', $ret);
     }
 
+    public function testGetEnvReturnsStringFromGlobalEnvBeforeServerIfPsrContainerHasNoEntry(): void
+    {
+        $psr = $this->createMock(ContainerInterface::class);
+        $psr->expects($this->atLeastOnce())->method('has')->with('X_FOO')->willReturn(false);
+        $psr->expects($this->never())->method('get');
+
+        assert($psr instanceof ContainerInterface);
+        $container = new Container($psr);
+
+        $_ENV['X_FOO'] = 'foo';
+        $_SERVER['X_FOO'] = 'bar';
+        $ret = $container->getEnv('X_FOO');
+        unset($_ENV['X_FOO'], $_SERVER['X_FOO']);
+
+        $this->assertEquals('foo', $ret);
+    }
+
+    public function testGetEnvReturnsStringFromGlobalEnvBeforeProcessEnvIfPsrContainerHasNoEntry(): void
+    {
+        $psr = $this->createMock(ContainerInterface::class);
+        $psr->expects($this->atLeastOnce())->method('has')->with('X_FOO')->willReturn(false);
+        $psr->expects($this->never())->method('get');
+
+        assert($psr instanceof ContainerInterface);
+        $container = new Container($psr);
+
+        $_ENV['X_FOO'] = 'foo';
+        putenv('X_FOO=bar');
+        $ret = $container->getEnv('X_FOO');
+        unset($_ENV['X_FOO']);
+        putenv('X_FOO');
+
+        $this->assertEquals('foo', $ret);
+    }
+
     public function testGetEnvThrowsIfMapContainsInvalidType(): void
     {
         $container = new Container([