diff --git a/src/Proxy/ProxyGenerator.php b/src/Proxy/ProxyGenerator.php
index 70d64bed1..8adbf5dc4 100644
--- a/src/Proxy/ProxyGenerator.php
+++ b/src/Proxy/ProxyGenerator.php
@@ -44,11 +44,14 @@
 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;
 use function sprintf;
 use function str_replace;
+use function strpos;
 use function strrev;
 use function strtolower;
 use function strtr;
@@ -58,6 +61,7 @@
 
 use const DIRECTORY_SEPARATOR;
 use const PHP_VERSION_ID;
+use const PREG_SPLIT_DELIM_CAPTURE;
 
 /**
  * This factory is used to generate proxy classes.
@@ -1124,6 +1128,17 @@ private function getParameterDefaultValue(ReflectionParameter $parameter)
 
         $value = rtrim(substr(explode('$' . $parameter->getName() . ' = ', (string) $parameter, 2)[1], 0, -2));
 
+        if (strpos($value, '\\') !== false || strpos($value, '::') !== false) {
+            $value = preg_split("/('(?:[^'\\\\]*+(?:\\\\.)*+)*+')/", $value, -1, PREG_SPLIT_DELIM_CAPTURE);
+            foreach ($value as $i => $part) {
+                if ($i % 2 === 0) {
+                    $value[$i] = preg_replace('/(?<![a-zA-Z0-9_\x7f-\xff\\\\])[a-zA-Z0-9_\x7f-\xff]++(?:\\\\[a-zA-Z0-9_\x7f-\xff]++|::)++/', '\\\\\0', $part);
+                }
+            }
+
+            $value = implode('', $value);
+        }
+
         return ' = ' . $value;
     }
 
diff --git a/tests/Common/Proxy/PHP81NewInInitializers.php b/tests/Common/Proxy/PHP81NewInInitializers.php
index d9c40da87..82f54cf41 100644
--- a/tests/Common/Proxy/PHP81NewInInitializers.php
+++ b/tests/Common/Proxy/PHP81NewInInitializers.php
@@ -4,6 +4,8 @@
 
 namespace Doctrine\Tests\Common\Proxy;
 
+use Doctrine\Tests\Common\Util\TestAsset\ConstProvider;
+
 class PHP81NewInInitializers
 {
     public function onlyInitializer($foo = new \stdClass()): void
@@ -20,4 +22,9 @@ public function arrayInDefault(array $foo = [new \DateTimeImmutable('2022-08-22
     {
 
     }
+
+    public function constInDefault(string $foo = ConstProvider::FOO): void
+    {
+
+    }
 }
diff --git a/tests/Common/Proxy/ProxyGeneratorTest.php b/tests/Common/Proxy/ProxyGeneratorTest.php
index dde498847..4322be43c 100644
--- a/tests/Common/Proxy/ProxyGeneratorTest.php
+++ b/tests/Common/Proxy/ProxyGeneratorTest.php
@@ -600,6 +600,11 @@ public function testPhp81NewInInitializers()
             'arrayInDefault(array $foo = [new \DateTimeImmutable(\'2022-08-22 16:20\', new \DateTimeZone(\'Europe/Warsaw\'))]): void',
             file_get_contents(__DIR__ . '/generated/__CG__DoctrineTestsCommonProxyPHP81NewInInitializers.php')
         );
+
+        self::assertStringContainsString(
+            'constInDefault(string $foo = \Doctrine\Tests\Common\Util\TestAsset\ConstProvider::FOO): void',
+            file_get_contents(__DIR__ . '/generated/__CG__DoctrineTestsCommonProxyPHP81NewInInitializers.php')
+        );
     }
 
     /**
diff --git a/tests/Common/Util/TestAsset/ConstProvider.php b/tests/Common/Util/TestAsset/ConstProvider.php
new file mode 100644
index 000000000..5f121efed
--- /dev/null
+++ b/tests/Common/Util/TestAsset/ConstProvider.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\Common\Util\TestAsset;
+
+class ConstProvider
+{
+    public const FOO = 'foo';
+}