diff --git a/UPGRADE.md b/UPGRADE.md
index 5bf1ef0a..79288df4 100644
--- a/UPGRADE.md
+++ b/UPGRADE.md
@@ -6,6 +6,25 @@ awareness about deprecated code.
 - Use of our low-overhead runtime deprecation API, details:
   https://github.com/doctrine/deprecations/
 
+# Upgrade to 4.1
+
+## Added `ColocatedMappingDriver::$fileRegex`
+
+You can search for mapping files with regex:
+
+```php
+// Search for all files but ending with Test, Fixture, Service
+$driver->setFileRegex('/(?<!Test|Fixture|Service)\.php$/');
+```
+
+## Deprecated `ColocatedMappingDriver::$fileExtension`
+
+Property `Doctrine\Persistence\Mapping\Driver\ColocatedMappingDriver::$fileExtension` and methods `getFileExtension()`,
+`setFileExtension()` are deprecated.
+
+Use `Doctrine\Persistence\Mapping\Driver\ColocatedMappingDriver::$fileRegex` and `getFileRegex()`,
+`setFileRegex()` instead.
+
 # Upgrade to 4.0
 
 ## BC Break: Removed `StaticReflectionService`
diff --git a/src/Persistence/Mapping/Driver/ColocatedMappingDriver.php b/src/Persistence/Mapping/Driver/ColocatedMappingDriver.php
index 2e955694..f3b93717 100644
--- a/src/Persistence/Mapping/Driver/ColocatedMappingDriver.php
+++ b/src/Persistence/Mapping/Driver/ColocatedMappingDriver.php
@@ -8,9 +8,9 @@
 use FilesystemIterator;
 use RecursiveDirectoryIterator;
 use RecursiveIteratorIterator;
-use RecursiveRegexIterator;
 use ReflectionClass;
 use RegexIterator;
+use SplFileInfo;
 
 use function array_merge;
 use function array_unique;
@@ -21,6 +21,7 @@
 use function preg_match;
 use function preg_quote;
 use function realpath;
+use function sprintf;
 use function str_contains;
 use function str_replace;
 
@@ -43,8 +44,15 @@ trait ColocatedMappingDriver
      */
     protected array $excludePaths = [];
 
-    /** The file extension of mapping documents. */
-    protected string $fileExtension = '.php';
+    /** The regex used to match mapping files. */
+    protected string $fileRegex = '/\.php$/';
+
+    /**
+     * The file extension of mapping documents.
+     *
+     * @deprecated Use {@see $fileRegex} instead.
+     */
+    protected string|null $fileExtension = '.php';
 
     /**
      * Cache for getAllClassNames().
@@ -94,16 +102,38 @@ public function getExcludePaths(): array
         return $this->excludePaths;
     }
 
-    /** Gets the file extension used to look for mapping files under. */
-    public function getFileExtension(): string
+    /** Gets the file regex used to look for mapping files under. */
+    public function getFileRegex(): string
+    {
+        return $this->fileRegex;
+    }
+
+    /** Sets the file regex used to look for mapping files with. */
+    public function setFileRegex(string $fileRegex): void
+    {
+        $this->fileRegex     = $fileRegex;
+        $this->fileExtension = null;
+    }
+
+    /**
+     * Gets the file extension used to look for mapping files under.
+     *
+     * @deprecated Use {@see getFileRegex()} instead.
+     */
+    public function getFileExtension(): string|null
     {
         return $this->fileExtension;
     }
 
-    /** Sets the file extension used to look for mapping files under. */
+    /**
+     * Sets the file extension used to look for mapping files under.
+     *
+     * @deprecated Use {@see setFileRegex()} instead.
+     */
     public function setFileExtension(string $fileExtension): void
     {
         $this->fileExtension = $fileExtension;
+        $this->fileRegex     = sprintf('/%s$/', preg_quote($fileExtension, '/'));
     }
 
     /**
@@ -140,20 +170,22 @@ public function getAllClassNames(): array
                 throw MappingException::fileMappingDriversRequireConfiguredDirectoryPath($path);
             }
 
+            /** @var iterable<SplFileInfo> $iterator */
             $iterator = new RegexIterator(
                 new RecursiveIteratorIterator(
                     new RecursiveDirectoryIterator($path, FilesystemIterator::SKIP_DOTS),
                     RecursiveIteratorIterator::LEAVES_ONLY,
                 ),
-                '/^.+' . preg_quote($this->fileExtension) . '$/i',
-                RecursiveRegexIterator::GET_MATCH,
+                $this->fileRegex,
+                RegexIterator::MATCH,
             );
 
             foreach ($iterator as $file) {
-                $sourceFile = $file[0];
+                $sourceFile = $file->getPathname();
 
                 if (preg_match('(^phar:)i', $sourceFile) === 0) {
                     $sourceFile = realpath($sourceFile);
+                    assert($sourceFile !== false);
                 }
 
                 foreach ($this->excludePaths as $excludePath) {
diff --git a/tests/Persistence/Mapping/ColocatedMappingDriverTest.php b/tests/Persistence/Mapping/ColocatedMappingDriverTest.php
index cbb4fea6..ee4295d2 100644
--- a/tests/Persistence/Mapping/ColocatedMappingDriverTest.php
+++ b/tests/Persistence/Mapping/ColocatedMappingDriverTest.php
@@ -4,14 +4,16 @@
 
 namespace Doctrine\Tests\Persistence\Mapping;
 
+use Doctrine\EntityFixture;
 use Doctrine\Persistence\Mapping\ClassMetadata;
 use Doctrine\Persistence\Mapping\Driver\ColocatedMappingDriver;
 use Doctrine\Persistence\Mapping\Driver\MappingDriver;
-use Doctrine\TestClass;
+use Doctrine\Tests\Persistence\Mapping\_files\colocated\Entity;
+use Doctrine\Tests\Persistence\Mapping\_files\colocated\TestClass;
 use Generator;
 use PHPUnit\Framework\TestCase;
 
-use function array_values;
+use function sort;
 
 class ColocatedMappingDriverTest extends TestCase
 {
@@ -44,6 +46,18 @@ public function testAddGetExcludePaths(): void
         ], $driver->getExcludePaths());
     }
 
+    public function testGetSetFileRegex(): void
+    {
+        $driver = $this->createDriver(__DIR__ . '/_files/colocated');
+        self::assertSame('/\.php$/', $driver->getFileRegex());
+
+        $driver->setFileRegex('/\.php1$/');
+
+        self::assertSame('/\.php1$/', $driver->getFileRegex());
+        self::assertNull($driver->getFileExtension());
+    }
+
+    /** @deprecated */
     public function testGetSetFileExtension(): void
     {
         $driver = $this->createDriver(__DIR__ . '/_files/colocated');
@@ -52,6 +66,7 @@ public function testGetSetFileExtension(): void
         $driver->setFileExtension('.php1');
 
         self::assertSame('.php1', $driver->getFileExtension());
+        self::assertSame('/\.php1$/', $driver->getFileRegex());
     }
 
     /** @dataProvider pathProvider */
@@ -61,7 +76,22 @@ public function testGetAllClassNames(string $path): void
 
         $classes = $driver->getAllClassNames();
 
-        self::assertSame([TestClass::class], $classes);
+        sort($classes);
+        self::assertSame([EntityFixture::class, Entity::class], $classes);
+    }
+
+    public function testGetAllClassNamesWithRegex(): void
+    {
+        $regex  = '/(?<!Fixture)\.php$/';
+        $driver = $this->createDriver(__DIR__ . '/_files/colocated', $regex);
+
+        $classes = $driver->getAllClassNames();
+
+        self::assertSame(
+            [Entity::class],
+            $classes,
+            'EntityFixture.php should be excluded by the regex, since it ends with Fixture suffix.',
+        );
     }
 
     /** @return Generator<string, array{string}> */
@@ -71,9 +101,9 @@ public static function pathProvider(): Generator
         yield 'winding path' => [__DIR__ . '/../Mapping/_files/colocated'];
     }
 
-    private function createDriver(string $path): MyDriver
+    private function createDriver(string $path, string|null $fileRegex = null): MyDriver
     {
-        return new MyDriver($path);
+        return new MyDriver([$path], $fileRegex);
     }
 }
 
@@ -81,10 +111,19 @@ final class MyDriver implements MappingDriver
 {
     use ColocatedMappingDriver;
 
-    /** @param string ...$paths One or multiple paths where mapping classes can be found. */
-    public function __construct(string ...$paths)
+    /**
+     * @param non-empty-list<string> $paths     One or multiple paths where mapping classes can be found.
+     * @param string|null            $fileRegex The regex used to look for mapping files with.
+     */
+    public function __construct(array $paths, string|null $fileRegex = null)
     {
-        $this->addPaths(array_values($paths));
+        $this->addPaths($paths);
+
+        if ($fileRegex === null) {
+            return;
+        }
+
+        $this->setFileRegex($fileRegex);
     }
 
     /**
@@ -96,6 +135,6 @@ public function loadMetadataForClass($className, ClassMetadata $metadata): void
 
     public function isTransient(string $className): bool
     {
-        return $className !== TestClass::class;
+        return $className === TestClass::class;
     }
 }
diff --git a/tests/Persistence/Mapping/_files/colocated/Entity.php b/tests/Persistence/Mapping/_files/colocated/Entity.php
new file mode 100644
index 00000000..352fe10e
--- /dev/null
+++ b/tests/Persistence/Mapping/_files/colocated/Entity.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\Persistence\Mapping\_files\colocated;
+
+class Entity
+{
+}
diff --git a/tests/Persistence/Mapping/_files/colocated/EntityFixture.php b/tests/Persistence/Mapping/_files/colocated/EntityFixture.php
new file mode 100644
index 00000000..5f044b7b
--- /dev/null
+++ b/tests/Persistence/Mapping/_files/colocated/EntityFixture.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine;
+
+class EntityFixture
+{
+}
diff --git a/tests/Persistence/Mapping/_files/colocated/Foo.mphp b/tests/Persistence/Mapping/_files/colocated/Foo.mphp
new file mode 100644
index 00000000..4fcfe63f
--- /dev/null
+++ b/tests/Persistence/Mapping/_files/colocated/Foo.mphp
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\Persistence\Mapping\_files\colocated;
+
+final class Foo
+{
+}
diff --git a/tests/Persistence/Mapping/_files/colocated/TestClass.php b/tests/Persistence/Mapping/_files/colocated/TestClass.php
index 19a373cc..bd3ccb71 100644
--- a/tests/Persistence/Mapping/_files/colocated/TestClass.php
+++ b/tests/Persistence/Mapping/_files/colocated/TestClass.php
@@ -2,12 +2,8 @@
 
 declare(strict_types=1);
 
-namespace Doctrine;
+namespace Doctrine\Tests\Persistence\Mapping\_files\colocated;
 
 class TestClass
 {
 }
-
-class Entity
-{
-}