diff --git a/src/DataMapper/ConstructorDataMapper.php b/src/DataMapper/ConstructorDataMapper.php
index 29740aa..5e7527b 100644
--- a/src/DataMapper/ConstructorDataMapper.php
+++ b/src/DataMapper/ConstructorDataMapper.php
@@ -13,6 +13,7 @@
 use ReflectionNamedType;
 use ReflectionProperty;
 use ReflectionType;
+use stdClass;
 
 use function array_filter;
 use function array_map;
@@ -93,7 +94,7 @@ public function generateToDataObject(DataMapperInterface $dataMapper): string
         $parametersCode = [];
 
         foreach ($parameters as $parameter) {
-            $parametersCode[$parameter->name] = new Expr(sprintf('$fields[%s] ?? %s', Code::value($parameter->name), Code::value($parameter->fallback)));
+            $parametersCode[$parameter->name] = new Expr(sprintf('$fields[%s] ?? %s', Code::value($parameter->name), $parameter->compiledFallback()));
         }
 
         $newDtoCode = Code::new($this->className, $parametersCode);
@@ -191,12 +192,18 @@ private function resolveFallbackValueFromType(?ReflectionType $type): mixed
             throw new LogicException(sprintf('Cannot use complex type with %s on %s', self::class, $this->className));
         }
 
+        if (!$type->isBuiltin()) {
+            // @phpstan-ignore-next-line
+            return (new ReflectionClass($type->getName()))->newInstanceWithoutConstructor();
+        }
+
         return match ($type->getName()) {
             'int' => 0,
             'float' => 0.0,
             'string' => '',
             'bool' => false,
             'array' => [],
+            'object' => new stdClass(),
             default => throw new LogicException(sprintf('Cannot resolve fallback value for type %s on %s', $type->getName(), $this->className)),
         };
     }
diff --git a/src/DataMapper/ConstructorParameterMetadata.php b/src/DataMapper/ConstructorParameterMetadata.php
index c04d543..6d09f07 100644
--- a/src/DataMapper/ConstructorParameterMetadata.php
+++ b/src/DataMapper/ConstructorParameterMetadata.php
@@ -2,6 +2,13 @@
 
 namespace Quatrevieux\Form\DataMapper;
 
+use Quatrevieux\Form\Util\Code;
+use Quatrevieux\Form\Util\Expr;
+use ReflectionClass;
+use stdClass;
+
+use function is_object;
+
 final class ConstructorParameterMetadata
 {
     public function __construct(
@@ -10,4 +17,13 @@ public function __construct(
         public readonly bool $required,
         public readonly string $requiredMessage,
     ) {}
+
+    public function compiledFallback(): string
+    {
+        if (is_object($this->fallback) && $this->fallback::class !== stdClass::class) {
+            return (string) Expr::new(ReflectionClass::class, [$this->fallback::class])->newInstanceWithoutConstructor();
+        }
+
+        return Code::value($this->fallback);
+    }
 }
diff --git a/tests/DataMapper/ConstructorDataMapperTest.php b/tests/DataMapper/ConstructorDataMapperTest.php
new file mode 100644
index 0000000..a9392e2
--- /dev/null
+++ b/tests/DataMapper/ConstructorDataMapperTest.php
@@ -0,0 +1,188 @@
+<?php
+
+namespace Quatrevieux\Form\DataMapper;
+
+use PHPUnit\Framework\TestCase;
+use Quatrevieux\Form\DataMapper\Generator\DataMapperGenerator;
+use Quatrevieux\Form\DefaultRegistry;
+use Quatrevieux\Form\Fixtures\EmbeddedFormConstructor;
+use Quatrevieux\Form\Fixtures\RequestWithDefaultValueConstructor;
+use Quatrevieux\Form\Fixtures\RequiredParametersRequestConstructor;
+use Quatrevieux\Form\Fixtures\SimpleRequestConstructor;
+use Quatrevieux\Form\Fixtures\WithEmbeddedConstructor;
+use Quatrevieux\Form\Validator\Constraint\Required;
+use stdClass;
+
+class ConstructorDataMapperTest extends TestCase
+{
+    public function test_empty(): void
+    {
+        $mapper = new ConstructorDataMapper(stdClass::class, new DefaultRegistry());
+
+        $dto = $mapper->toDataObject([]);
+
+        $this->assertSame(stdClass::class, $mapper->className());
+        $this->assertEquals(new stdClass(), $dto->dto);
+        $this->assertSame([], $dto->errors);
+        $this->assertSame([], $mapper->toArray($dto->dto));
+    }
+
+    public function test_nullable_parameters(): void
+    {
+        $mapper = new ConstructorDataMapper(SimpleRequestConstructor::class, new DefaultRegistry());
+
+        $empty = $mapper->toDataObject([]);
+
+        $this->assertSame([], $empty->errors);
+        $this->assertInstanceOf(SimpleRequestConstructor::class, $empty->dto);
+        $this->assertSame(null, $empty->dto->foo);
+        $this->assertSame(null, $empty->dto->bar);
+
+        $filled = $mapper->toDataObject(['foo' => 'abc', 'bar' => 'def']);
+
+        $this->assertSame([], $filled->errors);
+        $this->assertSame('abc', $filled->dto->foo);
+        $this->assertSame('def', $filled->dto->bar);
+        $this->assertSame(['foo' => 'abc', 'bar' => 'def'], $mapper->toArray($filled->dto));
+    }
+
+    public function test_default_values(): void
+    {
+        $mapper = new ConstructorDataMapper(RequestWithDefaultValueConstructor::class, new DefaultRegistry());
+
+        $dto = $mapper->toDataObject([]);
+
+        $this->assertSame([], $dto->errors);
+        $this->assertSame(42, $dto->dto->foo);
+        $this->assertSame('???', $dto->dto->bar);
+    }
+
+    public function test_required_parameters(): void
+    {
+        $mapper = new ConstructorDataMapper(RequiredParametersRequestConstructor::class, new DefaultRegistry());
+
+        $dto = $mapper->toDataObject([]);
+
+        $this->assertInstanceOf(RequiredParametersRequestConstructor::class, $dto->dto);
+        $this->assertSame(0, $dto->dto->foo);
+        $this->assertSame('', $dto->dto->bar);
+
+        $this->assertSame(['foo', 'bar'], array_keys($dto->errors));
+        $this->assertSame(Required::CODE, $dto->errors['foo']->code);
+        $this->assertSame(Required::CODE, $dto->errors['bar']->code);
+        $this->assertSame('This value is required', $dto->errors['foo']->message);
+        $this->assertSame('bar must be set', $dto->errors['bar']->message);
+
+        $filled = $mapper->toDataObject(['foo' => 12, 'bar' => 'value']);
+
+        $this->assertSame([], $filled->errors);
+        $this->assertSame(12, $filled->dto->foo);
+        $this->assertSame('value', $filled->dto->bar);
+    }
+
+    public function test_generate_to_array_code(): void
+    {
+        $mapper = new ConstructorDataMapper(SimpleRequestConstructor::class, new DefaultRegistry());
+
+        $this->assertSame('return get_object_vars($data);', $mapper->generateToArray($mapper));
+    }
+
+    public function test_generate_to_data_object_code(): void
+    {
+        $mapper = new ConstructorDataMapper(RequiredParametersRequestConstructor::class, new DefaultRegistry());
+
+        $this->assertSame(<<<'PHP'
+    $errors = [];
+    $dto = new \Quatrevieux\Form\Fixtures\RequiredParametersRequestConstructor(foo: $fields['foo'] ?? 0, bar: $fields['bar'] ?? '');
+
+    foreach (['foo' => 'This value is required', 'bar' => 'bar must be set'] as $field => $message) {
+        if (!isset($fields[$field])) {
+            $errors[$field] = new \Quatrevieux\Form\Validator\FieldError($message, [], 'b1ac3a70-06db-5cd6-8f0e-8e6b98b3fcb5', $this->registry->getTranslator());
+        }
+    }
+
+    return new \Quatrevieux\Form\DataMapper\DataMapperResult($dto, $errors);
+PHP, $mapper->generateToDataObject($mapper));
+    }
+
+    public function test_generated_mapper_code_and_runtime_behavior(): void
+    {
+        $generator = new DataMapperGenerator();
+        $mapper = new ConstructorDataMapper(SimpleRequestConstructor::class, new DefaultRegistry());
+        $code = $generator->generate('GeneratedSimpleRequestConstructorDataMapper', $mapper);
+
+        $this->assertNotNull($code);
+        $this->assertStringContainsString('class GeneratedSimpleRequestConstructorDataMapper implements Quatrevieux\\Form\\DataMapper\\DataMapperInterface', $code);
+        $this->assertStringContainsString('return Quatrevieux\\Form\\Fixtures\\SimpleRequestConstructor::class;', $code);
+        $this->assertStringContainsString('return get_object_vars($data);', $code);
+
+        eval(str_replace('<?php', '', $code));
+
+        /** @var DataMapperInterface $generatedMapper */
+        $generatedMapper = new \GeneratedSimpleRequestConstructorDataMapper(new DefaultRegistry());
+        $dto = $generatedMapper->toDataObject(['foo' => 'gen-foo', 'bar' => 'gen-bar']);
+
+        $this->assertSame([], $dto->errors);
+        $this->assertSame('gen-foo', $dto->dto->foo);
+        $this->assertSame('gen-bar', $dto->dto->bar);
+        $this->assertSame(['foo' => 'gen-foo', 'bar' => 'gen-bar'], $generatedMapper->toArray($dto->dto));
+    }
+
+    public function test_with_embedded()
+    {
+        $mapper = new ConstructorDataMapper(WithEmbeddedConstructor::class, new DefaultRegistry());
+
+        $dto = $mapper->toDataObject([]);
+
+        $this->assertSame(WithEmbeddedConstructor::class, $mapper->className());
+        $this->assertInstanceOf(WithEmbeddedConstructor::class, $dto->dto);
+
+        $this->assertSame('', $dto->dto->foo);
+        $this->assertSame('', $dto->dto->bar);
+        $this->assertInstanceOf(EmbeddedFormConstructor::class, $dto->dto->embedded);
+        $this->assertFalse(isset($dto->dto->embedded->baz));
+        $this->assertFalse(isset($dto->dto->embedded->rab));
+
+        $this->assertCount(3, $dto->errors);
+        $this->assertEquals('This value is required', (string) $dto->errors['foo']);
+        $this->assertEquals('This value is required', (string) $dto->errors['bar']);
+        $this->assertEquals('This value is required', (string) $dto->errors['embedded']);
+
+
+        $dto = $mapper->toDataObject([
+            'foo' => 'azerty',
+            'bar' => 'uiop',
+            'embedded' => new EmbeddedFormConstructor(
+                baz: 'qsdfgh',
+                rab: 'jklm',
+            ),
+        ]);
+
+        $this->assertEquals(new WithEmbeddedConstructor(
+            foo: 'azerty',
+            bar: 'uiop',
+            embedded: new EmbeddedFormConstructor(
+                baz: 'qsdfgh',
+                rab: 'jklm',
+            )
+        ), $dto->dto);
+
+        $this->assertEmpty($dto->errors);
+
+        $this->assertSame(
+            <<<'PHP'
+                $errors = [];
+                $dto = new \Quatrevieux\Form\Fixtures\WithEmbeddedConstructor(foo: $fields['foo'] ?? '', bar: $fields['bar'] ?? '', embedded: $fields['embedded'] ?? (new \ReflectionClass('Quatrevieux\\Form\\Fixtures\\EmbeddedFormConstructor'))->newInstanceWithoutConstructor());
+
+                foreach (['foo' => 'This value is required', 'bar' => 'This value is required', 'embedded' => 'This value is required'] as $field => $message) {
+                    if (!isset($fields[$field])) {
+                        $errors[$field] = new \Quatrevieux\Form\Validator\FieldError($message, [], 'b1ac3a70-06db-5cd6-8f0e-8e6b98b3fcb5', $this->registry->getTranslator());
+                    }
+                }
+
+                return new \Quatrevieux\Form\DataMapper\DataMapperResult($dto, $errors);
+            PHP,
+            $mapper->generateToDataObject($mapper)
+        );
+    }
+}
diff --git a/tests/Fixtures/WithEmbeddedConstructor.php b/tests/Fixtures/WithEmbeddedConstructor.php
new file mode 100644
index 0000000..a392ce8
--- /dev/null
+++ b/tests/Fixtures/WithEmbeddedConstructor.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace Quatrevieux\Form\Fixtures;
+
+use Quatrevieux\Form\Embedded\Embedded;
+
+class WithEmbeddedConstructor
+{
+    public function __construct(
+        public string $foo,
+        public string $bar,
+        #[Embedded(EmbeddedFormConstructor::class)]
+        public EmbeddedFormConstructor $embedded,
+    ) {}
+}
+
+class EmbeddedFormConstructor
+{
+    public function __construct(
+        public ?string $baz,
+        public ?string $rab,
+    ) {}
+}