diff --git a/README.md b/README.md
index acd0c28..0d77863 100644
--- a/README.md
+++ b/README.md
@@ -90,6 +90,40 @@ $request = $decoder->decode(/** protobuf buffer here */, CreateUserRequest::clas
 echo $request->name;
 ```
 
+### Required fields
+
+`Reflector::map()` maps missing fields using property defaults when they exist.
+If a property is non-nullable and has no default value, it is treated as required.
+
+When one or more required properties are missing, decoding fails with `Thesis\Protobuf\Reflection\Exception\MappingError`.
+The exception contains all reasons in `->reasons` (each reason is typically `PropertyRequired`).
+
+This behavior is aligned with other protobuf implementations/plugins: messages missing required fields are treated as invalid during decode.
+
+A field is considered required when either:
+- it is defined as `required` in `proto2`;
+- it is defined in editions with `features.field_presence = LEGACY_REQUIRED`.
+
+```php
+use Thesis\Protobuf\Decoder;
+use Thesis\Protobuf\Reflection;
+
+$decoder = Decoder\Builder::buildDefault();
+
+try {
+    $message = $decoder->decode($buffer, CreateUserRequest::class);
+} catch (Reflection\Exception\MappingError $e) {
+    foreach ($e->reasons as $reason) {
+        if ($reason instanceof Reflection\Exception\PropertyRequired) {
+            echo $reason->class . "::$" . $reason->property . PHP_EOL;
+        }
+    }
+}
+```
+
+Both `Encoder::encode()` and `Decoder::decode()` throw `Thesis\Protobuf\ProtobufException`.
+Domain protobuf exceptions are preserved and are not wrapped into generic runtime errors.
+
 ### Unknown fields
 
 When a protobuf message is decoded, it may contain fields that are not defined in the target class.
diff --git a/src/Decoder.php b/src/Decoder.php
index 2ba269e..f14aee4 100644
--- a/src/Decoder.php
+++ b/src/Decoder.php
@@ -4,8 +4,6 @@
 
 namespace Thesis\Protobuf;
 
-use Thesis\Protobuf\Decoder\DecodingError;
-
 /**
  * @api
  */
@@ -15,7 +13,7 @@ interface Decoder
      * @template T of object
      * @param class-string<T> $classType
      * @return T
-     * @throws DecodingError
+     * @throws ProtobufException
      */
     public function decode(string $buffer, string $classType): object;
 }
diff --git a/src/Decoder/Internal/ReflectionDecoder.php b/src/Decoder/Internal/ReflectionDecoder.php
index 0348353..f952bb9 100644
--- a/src/Decoder/Internal/ReflectionDecoder.php
+++ b/src/Decoder/Internal/ReflectionDecoder.php
@@ -5,6 +5,7 @@
 namespace Thesis\Protobuf\Decoder\Internal;
 
 use Thesis\Protobuf\Decoder;
+use Thesis\Protobuf\ProtobufException;
 use Thesis\Protobuf\Reflection\Reflector;
 use Thesis\Protobuf\Serializer;
 
@@ -29,6 +30,8 @@ public function decode(string $buffer, string $classType): object
                 ),
                 $classType,
             );
+        } catch (ProtobufException $e) {
+            throw $e;
         } catch (\Throwable $e) {
             throw new Decoder\DecodingError($e->getMessage(), (int) $e->getCode(), $e);
         }
diff --git a/src/Encoder.php b/src/Encoder.php
index b799921..4a45fd5 100644
--- a/src/Encoder.php
+++ b/src/Encoder.php
@@ -4,15 +4,13 @@
 
 namespace Thesis\Protobuf;
 
-use Thesis\Protobuf\Encoder\EncodingError;
-
 /**
  * @api
  */
 interface Encoder
 {
     /**
-     * @throws EncodingError
+     * @throws ProtobufException
      */
     public function encode(object $message): string;
 }
diff --git a/src/Encoder/Internal/ReflectionEncoder.php b/src/Encoder/Internal/ReflectionEncoder.php
index 878744d..60d559d 100644
--- a/src/Encoder/Internal/ReflectionEncoder.php
+++ b/src/Encoder/Internal/ReflectionEncoder.php
@@ -5,6 +5,7 @@
 namespace Thesis\Protobuf\Encoder\Internal;
 
 use Thesis\Protobuf\Encoder;
+use Thesis\Protobuf\ProtobufException;
 use Thesis\Protobuf\Reflection\Reflector;
 use Thesis\Protobuf\Serializer;
 
@@ -25,6 +26,8 @@ public function encode(object $message): string
             return $this->serializer->serialize(
                 $this->reflector->message($message),
             );
+        } catch (ProtobufException $e) {
+            throw $e;
         } catch (\Throwable $e) {
             throw new Encoder\EncodingError($e->getMessage(), (int) $e->getCode(), $e);
         }
diff --git a/src/Reflection/Exception/MappingError.php b/src/Reflection/Exception/MappingError.php
new file mode 100644
index 0000000..972df55
--- /dev/null
+++ b/src/Reflection/Exception/MappingError.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Thesis\Protobuf\Reflection\Exception;
+
+use Thesis\Protobuf\Reflection\ReflectionException;
+
+/**
+ * @api
+ */
+final class MappingError extends ReflectionException
+{
+    /**
+     * @param non-empty-list<ReflectionException> $reasons
+     */
+    public function __construct(
+        public readonly array $reasons,
+    ) {
+        parent::__construct(\sprintf(
+            'Multiple exceptions encountered (%d): %s',
+            \count($reasons),
+            implode('', array_map(
+                static fn(ReflectionException $reason) => \sprintf("\n\n%s: %s", $reason::class, $reason->getMessage()),
+                $this->reasons,
+            )),
+        ));
+    }
+}
diff --git a/src/Reflection/Exception/PropertyRequired.php b/src/Reflection/Exception/PropertyRequired.php
new file mode 100644
index 0000000..d1bf41a
--- /dev/null
+++ b/src/Reflection/Exception/PropertyRequired.php
@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Thesis\Protobuf\Reflection\Exception;
+
+use Thesis\Protobuf\Reflection\ReflectionException;
+
+/**
+ * @api
+ */
+final class PropertyRequired extends ReflectionException
+{
+    /**
+     * @param non-empty-string $class
+     * @param non-empty-string $property
+     */
+    public function __construct(
+        public readonly string $class,
+        public readonly string $property,
+    ) {
+        parent::__construct(\sprintf('The property "%s::$%s" is required and cannot be initialized implicitly.', $class, $property));
+    }
+}
diff --git a/src/Reflection/Exception/PropertyUninitialized.php b/src/Reflection/Exception/PropertyUninitialized.php
deleted file mode 100644
index 696e6f0..0000000
--- a/src/Reflection/Exception/PropertyUninitialized.php
+++ /dev/null
@@ -1,26 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Thesis\Protobuf\Reflection\Exception;
-
-use Thesis\Protobuf\Reflection\ReflectionException;
-
-/**
- * @api
- */
-final class PropertyUninitialized extends ReflectionException
-{
-    /**
-     * @param non-empty-string $class
-     * @param non-empty-string $propertyName
-     */
-    public function __construct(string $class, string $propertyName, int $code = 0, ?\Throwable $previous = null)
-    {
-        parent::__construct(
-            "Property `{$class}::\${$propertyName}` cannot be initialized: make it nullable or provide a default value.",
-            $code,
-            $previous,
-        );
-    }
-}
diff --git a/src/Reflection/Internal/Visitor/ToDefaultValueTypeVisitor.php b/src/Reflection/Internal/Visitor/ToDefaultValueTypeVisitor.php
deleted file mode 100644
index e0ccb1f..0000000
--- a/src/Reflection/Internal/Visitor/ToDefaultValueTypeVisitor.php
+++ /dev/null
@@ -1,99 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Thesis\Protobuf\Reflection\Internal\Visitor;
-
-use Thesis\Protobuf\Map;
-use Thesis\Protobuf\Reflection\BoolT;
-use Thesis\Protobuf\Reflection\BytesT;
-use Thesis\Protobuf\Reflection\DoubleT;
-use Thesis\Protobuf\Reflection\EnumT;
-use Thesis\Protobuf\Reflection\Fixed32T;
-use Thesis\Protobuf\Reflection\FloatT;
-use Thesis\Protobuf\Reflection\ListT;
-use Thesis\Protobuf\Reflection\MapT;
-use Thesis\Protobuf\Reflection\SFixed32T;
-use Thesis\Protobuf\Reflection\StringT;
-use Thesis\Protobuf\Reflection\Type;
-
-/**
- * @internal
- * @template-extends DefaultTypeVisitor<mixed>
- */
-final class ToDefaultValueTypeVisitor extends DefaultTypeVisitor
-{
-    #[\Override]
-    public function bool(BoolT $type): mixed
-    {
-        return false;
-    }
-
-    #[\Override]
-    public function float(FloatT $type): mixed
-    {
-        return 0;
-    }
-
-    #[\Override]
-    public function double(DoubleT $type): mixed
-    {
-        return 0;
-    }
-
-    #[\Override]
-    public function fixed32(Fixed32T $type): mixed
-    {
-        return 0;
-    }
-
-    #[\Override]
-    public function sfixed32(SFixed32T $type): mixed
-    {
-        return 0;
-    }
-
-    #[\Override]
-    public function string(StringT $type): mixed
-    {
-        return '';
-    }
-
-    #[\Override]
-    public function bytes(BytesT $type): mixed
-    {
-        return '';
-    }
-
-    #[\Override]
-    public function list(ListT $type): mixed
-    {
-        return [];
-    }
-
-    #[\Override]
-    public function map(MapT $type): mixed
-    {
-        return new Map();
-    }
-
-    #[\Override]
-    public function enum(EnumT $type): mixed
-    {
-        $cases = $type->enum::cases();
-
-        foreach ($cases as $case) {
-            if ($case->value === 0) {
-                return $case;
-            }
-        }
-
-        return null;
-    }
-
-    #[\Override]
-    protected function default(Type $type): null
-    {
-        return null;
-    }
-}
diff --git a/src/Reflection/ReflectionException.php b/src/Reflection/ReflectionException.php
index 2abaf28..5db431e 100644
--- a/src/Reflection/ReflectionException.php
+++ b/src/Reflection/ReflectionException.php
@@ -4,7 +4,9 @@
 
 namespace Thesis\Protobuf\Reflection;
 
+use Thesis\Protobuf\ProtobufException;
+
 /**
  * @api
  */
-abstract class ReflectionException extends \Exception {}
+abstract class ReflectionException extends ProtobufException {}
diff --git a/src/Reflection/Reflector.php b/src/Reflection/Reflector.php
index 9679ad2..5e8d8da 100644
--- a/src/Reflection/Reflector.php
+++ b/src/Reflection/Reflector.php
@@ -8,12 +8,10 @@
 use Thesis\Protobuf;
 use Thesis\Protobuf\Message;
 use Thesis\Protobuf\Reflection\Internal\Api\ClassReflector;
-use Thesis\Protobuf\Reflection\Internal\Api\PropertyReflection;
 use Thesis\Protobuf\Reflection\Internal\Cache\Cache;
 use Thesis\Protobuf\Reflection\Internal\Cache\InMemoryPsr16Cache;
 use Thesis\Protobuf\Reflection\Internal\Visitor\IsValueEmpty;
 use Thesis\Protobuf\Reflection\Internal\Visitor\RecursionBreakTypeVisitor;
-use Thesis\Protobuf\Reflection\Internal\Visitor\ToDefaultValueTypeVisitor;
 use Thesis\Protobuf\Reflection\Internal\Visitor\ToProtobufTypeTypeVisitor;
 use Thesis\Protobuf\Reflection\Internal\Visitor\ToProtobufValueTypeVisitor;
 use Thesis\Protobuf\Reflection\Internal\Visitor\ToValueTypeVisitor;
@@ -30,8 +28,6 @@ final class Reflector
     /** @var ToProtobufValueTypeVisitor<*> */
     private readonly ToProtobufValueTypeVisitor $valueVisitor;
 
-    private readonly ToDefaultValueTypeVisitor $defaultValueTypeVisitor;
-
     private readonly ClassReflector $classReflector;
 
     /** @var array<class-string, true> */
@@ -55,7 +51,6 @@ private function __construct(
     ) {
         $this->typeVisitor = new ToProtobufTypeTypeVisitor($this);
         $this->valueVisitor = new ToProtobufValueTypeVisitor($this);
-        $this->defaultValueTypeVisitor = new ToDefaultValueTypeVisitor();
         $this->classReflector = new ClassReflector();
     }
 
@@ -123,6 +118,8 @@ public function map(Message $message, string $class): object
         $classReflection = $this->classReflector->reflect($class);
         $object = $classReflection->class->newInstanceWithoutConstructor();
 
+        $exceptions = [];
+
         foreach ($classReflection->properties as $property) {
             $propertyType = $property->reflection->getType();
             \assert($propertyType !== null);
@@ -130,18 +127,27 @@ public function map(Message $message, string $class): object
             if ($property->attributes->has(Field::class)) {
                 $field = $property->attributes->get(Field::class);
 
-                $descriptor = $message->fields[$field->num] ?? null;
+                if (isset($message->fields[$field->num])) {
+                    $value = $field
+                        ->type
+                        ->accept(new ToValueTypeVisitor(
+                            $this,
+                            $message->fields[$field->num]->value->value,
+                        ));
+                } elseif ($property->default !== null) {
+                    $value = $property->default->value;
+                } else {
+                    $exceptions[] = new Exception\PropertyRequired(
+                        $property->reflection->getDeclaringClass()->getName(),
+                        $property->reflection->getName(),
+                    );
+
+                    continue;
+                }
+
                 $property->reflection->setValue(
                     $object,
-                    match (true) {
-                        $descriptor !== null => $field
-                            ->type
-                            ->accept(new ToValueTypeVisitor(
-                                $this,
-                                $descriptor->value->value,
-                            )),
-                        default => $this->defaultValuePropertyValue($property, $field),
-                    },
+                    $value,
                 );
             } elseif ($property->attributes->has(OneOf::class)) {
                 $oneof = $property->attributes->get(OneOf::class);
@@ -163,11 +169,15 @@ public function map(Message $message, string $class): object
 
                 $property->reflection->setValue(
                     $object,
-                    $this->defaultValuePropertyValue($property),
+                    null,
                 );
             }
         }
 
+        if ($exceptions !== []) {
+            throw new Exception\MappingError($exceptions);
+        }
+
         if ($message->unknowns !== []) {
             $this->unknowns?->handle($object, $message->unknowns);
         }
@@ -220,19 +230,4 @@ private function doGetMessage(object $message, ?\Closure $presence = null): Mess
 
         return Protobuf\message(...$descriptors);
     }
-
-    /**
-     * @throws Exception\PropertyUninitialized
-     */
-    private function defaultValuePropertyValue(PropertyReflection $property, ?Field $field = null): mixed
-    {
-        if ($property->default !== null) {
-            return $property->default->value;
-        }
-
-        return $field?->type->accept($this->defaultValueTypeVisitor) ?? throw new Exception\PropertyUninitialized(
-            $property->reflection->getDeclaringClass()->getName(),
-            $property->reflection->getName(),
-        );
-    }
 }
diff --git a/tests/Decoder/Internal/ReflectionDecoderTest.php b/tests/Decoder/Internal/ReflectionDecoderTest.php
index 1c8e058..516f5fa 100644
--- a/tests/Decoder/Internal/ReflectionDecoderTest.php
+++ b/tests/Decoder/Internal/ReflectionDecoderTest.php
@@ -20,6 +20,18 @@ public function testDecode(): void
         self::assertIsString($buffer);
         self::assertEquals(new Request('John Doe', 50), $decoder->decode($buffer, Request::class));
     }
+
+    public function testRequiredPropertiesCannotBeInitializedImplicitly(): void
+    {
+        $decoder = Builder::buildDefault();
+
+        $this->expectExceptionObject(new Reflection\Exception\MappingError([
+            new Reflection\Exception\PropertyRequired(Request::class, 'name'),
+            new Reflection\Exception\PropertyRequired(Request::class, 'id'),
+        ]));
+
+        $decoder->decode('', Request::class);
+    }
 }
 
 final readonly class Request
diff --git a/tests/testdata/reflection/oneof.php b/tests/testdata/reflection/oneof.php
index 9b7e259..ed73b06 100644
--- a/tests/testdata/reflection/oneof.php
+++ b/tests/testdata/reflection/oneof.php
@@ -10,7 +10,7 @@ interface DeveloperContact {}
 {
     public function __construct(
         #[Reflection\Field(3, Reflection\StringT::T)]
-        public string $email,
+        public string $email = '',
     ) {}
 }
 
@@ -18,7 +18,7 @@ public function __construct(
 {
     public function __construct(
         #[Reflection\Field(4, Reflection\StringT::T)]
-        public string $phone,
+        public string $phone = '',
     ) {}
 }
 
@@ -26,7 +26,7 @@ public function __construct(
 {
     public function __construct(
         #[Reflection\Field(5, new Reflection\ObjectT(Chat::class))]
-        public Chat $chat,
+        public ?Chat $chat = null,
     ) {}
 }
 
@@ -34,26 +34,27 @@ public function __construct(
 {
     public function __construct(
         #[Reflection\Field(1, Reflection\Int32T::T)]
-        public int $id,
+        public int $id = 0,
         #[Reflection\Field(2, Reflection\StringT::T)]
-        public string $username,
+        public string $username = '',
     ) {}
 }
 
 enum Role: int
 {
-    case ROLE_MEMBER = 0;
-    case ROLE_MAINTAINER = 1;
-    case ROLE_OWNER = 2;
+    case ROLE_UNSPECIFIED = 0;
+    case ROLE_MEMBER = 1;
+    case ROLE_MAINTAINER = 2;
+    case ROLE_OWNER = 3;
 }
 
 final readonly class Organization
 {
     public function __construct(
         #[Reflection\Field(1, Reflection\StringT::T)]
-        public string $name,
+        public string $name = '',
         #[Reflection\Field(2, new Reflection\EnumT(Role::class))]
-        public Role $role,
+        public Role $role = Role::ROLE_UNSPECIFIED,
     ) {}
 }
 
@@ -64,22 +65,22 @@ public function __construct(
      */
     public function __construct(
         #[Reflection\Field(1, Reflection\StringT::T)]
-        public string $name,
+        public string $name = '',
         #[Reflection\Field(
             2,
             new Reflection\ListT(
                 new Reflection\ObjectT(Organization::class),
             ),
         )]
-        public array $organizations,
+        public array $organizations = [],
         #[Reflection\Field(6, Reflection\StringT::T)]
-        public string $url,
+        public string $url = '',
         #[Reflection\OneOf([
             EmailContact::class,
             PhoneContact::class,
             TelegramContact::class,
         ])]
-        public DeveloperContact $contact,
+        public ?DeveloperContact $contact = null,
     ) {}
 }
 
diff --git a/tests/testdata/reflection/oneof.proto b/tests/testdata/reflection/oneof.proto
index 41b53ca..4e52574 100644
--- a/tests/testdata/reflection/oneof.proto
+++ b/tests/testdata/reflection/oneof.proto
@@ -11,9 +11,10 @@ message Organization {
   string name = 1;
 
   enum Role {
-    ROLE_MEMBER = 0;
-    ROLE_MAINTAINER = 1;
-    ROLE_OWNER = 2;
+    ROLE_UNSPECIFIED = 0;
+    ROLE_MEMBER = 1;
+    ROLE_MAINTAINER = 2;
+    ROLE_OWNER = 3;
   };
   Role role = 2;
 }