diff --git a/lib/Doctrine/Common/Proxy/ProxyGenerator.php b/lib/Doctrine/Common/Proxy/ProxyGenerator.php
index ec904312f..a3c431e37 100644
--- a/lib/Doctrine/Common/Proxy/ProxyGenerator.php
+++ b/lib/Doctrine/Common/Proxy/ProxyGenerator.php
@@ -44,6 +44,8 @@
 use function mkdir;
 use function preg_match;
 use function preg_match_all;
+use function preg_replace;
+use function preg_split;
 use function random_bytes;
 use function rename;
 use function rtrim;
@@ -58,6 +60,7 @@
 
 use const DIRECTORY_SEPARATOR;
 use const PHP_VERSION_ID;
+use const PREG_SPLIT_DELIM_CAPTURE;
 
 /**
  * This factory is used to generate proxy classes.
@@ -1089,10 +1092,7 @@ private function buildParametersString(array $parameters, array $renameParameter
             }
 
             $parameterDefinition .= '$' . ($renameParameters ? $renameParameters[$i] : $param->getName());
-
-            if ($param->isDefaultValueAvailable()) {
-                $parameterDefinition .= ' = ' . var_export($param->getDefaultValue(), true);
-            }
+            $parameterDefinition .= $this->getParameterDefaultValue($param);
 
             $parameterDefinitions[] = $parameterDefinition;
         }
@@ -1116,6 +1116,30 @@ private function getParameterType(ReflectionParameter $parameter)
         return $this->formatType($parameter->getType(), $declaringFunction, $parameter);
     }
 
+    private function getParameterDefaultValue(ReflectionParameter $parameter)
+    {
+        if (! $parameter->isDefaultValueAvailable()) {
+            return '';
+        }
+
+        if (PHP_VERSION_ID < 80100) {
+            return ' = ' . var_export($parameter->getDefaultValue(), true);
+        }
+
+        $value = rtrim(substr(explode('$' . $parameter->getName() . ' = ', (string) $parameter, 2)[1], 0, -2));
+        $parts = preg_split('{(\'(?:[^\'\\\\]*(?:\\\\.[^\'\\\\]*)*)\')}', $value, -1, PREG_SPLIT_DELIM_CAPTURE);
+
+        foreach ($parts as $i => &$part) {
+            if ($part === '' || $i % 2 !== 0) {
+                continue;
+            }
+
+            $part = preg_replace('/(?(DEFINE)(?<V>[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*+))(?<!\\\\)(?&V)(?:\\\\(?&V))*+::/', '\\\\$0', $part);
+        }
+
+        return ' = ' . implode('', $parts);
+    }
+
     /**
      * @param ReflectionParameter[] $parameters
      *
diff --git a/tests/Doctrine/Tests/Common/Proxy/PHP81NewInInitializers.php b/tests/Doctrine/Tests/Common/Proxy/PHP81NewInInitializers.php
new file mode 100644
index 000000000..dc0d79c64
--- /dev/null
+++ b/tests/Doctrine/Tests/Common/Proxy/PHP81NewInInitializers.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\Common\Proxy;
+
+class PHP81NewInInitializers
+{
+    public function onlyInitializer($foo = new \stdClass()): void
+    {
+
+    }
+
+    public function typed(\DateTimeInterface $foo = new \DateTimeImmutable('now')): void
+    {
+
+    }
+}
diff --git a/tests/Doctrine/Tests/Common/Proxy/ProxyGeneratorTest.php b/tests/Doctrine/Tests/Common/Proxy/ProxyGeneratorTest.php
index 1d2841cdd..09eba6fd2 100644
--- a/tests/Doctrine/Tests/Common/Proxy/ProxyGeneratorTest.php
+++ b/tests/Doctrine/Tests/Common/Proxy/ProxyGeneratorTest.php
@@ -552,6 +552,31 @@ public function testEnumDefaultInPublicProperty() : void
         $this->assertSame($object->isEnum, \Doctrine\Tests\Common\Proxy\YesOrNo::YES);
     }
 
+    /**
+     * @requires PHP >= 8.1.0
+     */
+    public function testPhp81NewInInitializers()
+    {
+        $className = PHP81NewInInitializers::class;
+
+        if (!class_exists('Doctrine\Tests\Common\ProxyProxy\__CG__\PHP81NewInInitializers', false)) {
+            $metadata = $this->createClassMetadata($className, ['id']);
+
+            $proxyGenerator = new ProxyGenerator(__DIR__ . '/generated', __NAMESPACE__ . 'Proxy');
+            $this->generateAndRequire($proxyGenerator, $metadata);
+        }
+
+        self::assertStringContainsString(
+            'onlyInitializer($foo = new \stdClass()): void',
+            file_get_contents(__DIR__ . '/generated/__CG__DoctrineTestsCommonProxyPHP81NewInInitializers.php')
+        );
+
+        self::assertStringContainsString(
+            'typed(\DateTimeInterface $foo = new \DateTimeImmutable(\'now\')): void',
+            file_get_contents(__DIR__ . '/generated/__CG__DoctrineTestsCommonProxyPHP81NewInInitializers.php')
+        );
+    }
+
     /**
      * @param string  $className
      * @param mixed[] $ids