diff --git a/CHANGELOG.md b/CHANGELOG.md
index ae90552..e5cc192 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 * refactor: Move transformer query logic to `TransformerRegistry`.
 * refactor: Mover more logic to `TransformerRegistry`.
 * refactor: Move `MainTransformer` to its own namespace.
+* refactor: Refactor exception.
 
 ## 0.5.4
 
diff --git a/src/Exception/UnableToFindSuitableTransformerException.php b/src/MainTransformer/Exception/CannotFindTransformerException.php
similarity index 72%
rename from src/Exception/UnableToFindSuitableTransformerException.php
rename to src/MainTransformer/Exception/CannotFindTransformerException.php
index 446429d..c54a50f 100644
--- a/src/Exception/UnableToFindSuitableTransformerException.php
+++ b/src/MainTransformer/Exception/CannotFindTransformerException.php
@@ -11,13 +11,13 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\MainTransformer\Exception;
 
 use Rekalogika\Mapper\Transformer\Contracts\MixedType;
 use Rekalogika\Mapper\Util\TypeUtil;
 use Symfony\Component\PropertyInfo\Type;
 
-class UnableToFindSuitableTransformerException extends NotMappableValueException
+class CannotFindTransformerException extends \RuntimeException
 {
     /**
      * @param array<int,Type|MixedType> $sourceTypes
@@ -28,6 +28,6 @@ public function __construct(array $sourceTypes, array $targetTypes)
         $sourceTypes = TypeUtil::getDebugType($sourceTypes);
         $targetTypes = TypeUtil::getDebugType($targetTypes);
 
-        parent::__construct(sprintf('Unable to find a suitable transformer for mapping the source types "%s" to the target types "%s"', $sourceTypes, $sourceTypes));
+        parent::__construct(sprintf('Cannot find a matching transformer for mapping the source types "%s" to the target types "%s"', $sourceTypes, $sourceTypes));
     }
 }
diff --git a/src/Exception/MapperReturnsUnexpectedValueException.php b/src/MainTransformer/Exception/TransformerReturnsUnexpectedValueException.php
similarity index 61%
rename from src/Exception/MapperReturnsUnexpectedValueException.php
rename to src/MainTransformer/Exception/TransformerReturnsUnexpectedValueException.php
index 7ca567a..6f0241d 100644
--- a/src/Exception/MapperReturnsUnexpectedValueException.php
+++ b/src/MainTransformer/Exception/TransformerReturnsUnexpectedValueException.php
@@ -11,18 +11,20 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\MainTransformer\Exception;
 
+use Rekalogika\Mapper\Exception\UnexpectedValueException;
+use Rekalogika\Mapper\Transformer\Contracts\MixedType;
 use Rekalogika\Mapper\Util\TypeUtil;
 use Symfony\Component\PropertyInfo\Type;
 
-class MapperReturnsUnexpectedValueException extends UnexpectedValueException
+class TransformerReturnsUnexpectedValueException extends UnexpectedValueException
 {
-    public function __construct(Type|null $type, mixed $target)
+    public function __construct(Type|MixedType $type, mixed $target)
     {
         $message = sprintf(
             'Mapper returns unexpected value. Expected type "%s", but got "%s"',
-            $type === null ? 'unknown' : TypeUtil::getTypeString($type),
+            TypeUtil::getTypeString($type),
             get_debug_type($target),
         );
 
diff --git a/src/MainTransformer/MainTransformer.php b/src/MainTransformer/MainTransformer.php
index 536cffa..c1d6059 100644
--- a/src/MainTransformer/MainTransformer.php
+++ b/src/MainTransformer/MainTransformer.php
@@ -14,7 +14,8 @@
 namespace Rekalogika\Mapper\MainTransformer;
 
 use Rekalogika\Mapper\Exception\LogicException;
-use Rekalogika\Mapper\Exception\UnableToFindSuitableTransformerException;
+use Rekalogika\Mapper\MainTransformer\Exception\CannotFindTransformerException;
+use Rekalogika\Mapper\MainTransformer\Exception\TransformerReturnsUnexpectedValueException;
 use Rekalogika\Mapper\ObjectCache\ObjectCache;
 use Rekalogika\Mapper\ObjectCache\ObjectCacheFactoryInterface;
 use Rekalogika\Mapper\Transformer\Contracts\MainTransformerAwareInterface;
@@ -22,6 +23,7 @@
 use Rekalogika\Mapper\Transformer\Contracts\TransformerInterface;
 use Rekalogika\Mapper\TransformerRegistry\TransformerRegistryInterface;
 use Rekalogika\Mapper\TypeResolver\TypeResolverInterface;
+use Rekalogika\Mapper\Util\TypeCheck;
 use Symfony\Component\PropertyInfo\Type;
 
 class MainTransformer implements MainTransformerInterface
@@ -150,9 +152,13 @@ public function transform(
                 context: $context
             );
 
+            if (!TypeCheck::isVariableInstanceOf($result, $targetType)) {
+                throw new TransformerReturnsUnexpectedValueException($targetType, $result);
+            }
+
             return $result;
         }
 
-        throw new UnableToFindSuitableTransformerException($sourceTypes, $targetTypes);
+        throw new CannotFindTransformerException($sourceTypes, $targetTypes);
     }
 }
diff --git a/src/Exception/CachedTargetObjectNotFoundException.php b/src/ObjectCache/Exception/CachedTargetObjectNotFoundException.php
similarity index 77%
rename from src/Exception/CachedTargetObjectNotFoundException.php
rename to src/ObjectCache/Exception/CachedTargetObjectNotFoundException.php
index c34e434..d45e825 100644
--- a/src/Exception/CachedTargetObjectNotFoundException.php
+++ b/src/ObjectCache/Exception/CachedTargetObjectNotFoundException.php
@@ -11,7 +11,9 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\ObjectCache\Exception;
+
+use Rekalogika\Mapper\Exception\RuntimeException;
 
 class CachedTargetObjectNotFoundException extends RuntimeException
 {
diff --git a/src/Exception/CircularReferenceException.php b/src/ObjectCache/Exception/CircularReferenceException.php
similarity index 74%
rename from src/Exception/CircularReferenceException.php
rename to src/ObjectCache/Exception/CircularReferenceException.php
index a709ccb..49d923a 100644
--- a/src/Exception/CircularReferenceException.php
+++ b/src/ObjectCache/Exception/CircularReferenceException.php
@@ -11,12 +11,14 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\ObjectCache\Exception;
 
+use Rekalogika\Mapper\Exception\ExceptionInterface;
+use Rekalogika\Mapper\Exception\RuntimeException;
 use Rekalogika\Mapper\Util\TypeUtil;
 use Symfony\Component\PropertyInfo\Type;
 
-class CircularReferenceException extends \RuntimeException implements ExceptionInterface
+class CircularReferenceException extends RuntimeException implements ExceptionInterface
 {
     public function __construct(mixed $source, Type $targetType)
     {
diff --git a/src/Exception/NonSimpleTypeException.php b/src/ObjectCache/Exception/NonSimpleTypeException.php
similarity index 84%
rename from src/Exception/NonSimpleTypeException.php
rename to src/ObjectCache/Exception/NonSimpleTypeException.php
index df56152..47040c8 100644
--- a/src/Exception/NonSimpleTypeException.php
+++ b/src/ObjectCache/Exception/NonSimpleTypeException.php
@@ -11,8 +11,9 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\ObjectCache\Exception;
 
+use Rekalogika\Mapper\Exception\UnexpectedValueException;
 use Rekalogika\Mapper\Util\TypeUtil;
 use Symfony\Component\PropertyInfo\Type;
 
diff --git a/src/ObjectCache/ObjectCache.php b/src/ObjectCache/ObjectCache.php
index 611c52e..6e7f9e2 100644
--- a/src/ObjectCache/ObjectCache.php
+++ b/src/ObjectCache/ObjectCache.php
@@ -13,10 +13,10 @@
 
 namespace Rekalogika\Mapper\ObjectCache;
 
-use Rekalogika\Mapper\Exception\CachedTargetObjectNotFoundException;
-use Rekalogika\Mapper\Exception\CircularReferenceException;
 use Rekalogika\Mapper\Exception\LogicException;
-use Rekalogika\Mapper\Exception\NonSimpleTypeException;
+use Rekalogika\Mapper\ObjectCache\Exception\CachedTargetObjectNotFoundException;
+use Rekalogika\Mapper\ObjectCache\Exception\CircularReferenceException;
+use Rekalogika\Mapper\ObjectCache\Exception\NonSimpleTypeException;
 use Rekalogika\Mapper\TypeResolver\TypeResolverInterface;
 use Symfony\Component\PropertyInfo\Type;
 
diff --git a/src/Transformer/ArrayToObjectTransformer.php b/src/Transformer/ArrayToObjectTransformer.php
index a383da0..b0d467b 100644
--- a/src/Transformer/ArrayToObjectTransformer.php
+++ b/src/Transformer/ArrayToObjectTransformer.php
@@ -14,9 +14,9 @@
 namespace Rekalogika\Mapper\Transformer;
 
 use Rekalogika\Mapper\Exception\InvalidArgumentException;
-use Rekalogika\Mapper\Exception\InvalidTypeInArgumentException;
 use Rekalogika\Mapper\Transformer\Contracts\TransformerInterface;
 use Rekalogika\Mapper\Transformer\Contracts\TypeMapping;
+use Rekalogika\Mapper\Transformer\Exception\InvalidTypeInArgumentException;
 use Rekalogika\Mapper\Util\TypeCheck;
 use Rekalogika\Mapper\Util\TypeFactory;
 use Symfony\Component\PropertyInfo\Type;
diff --git a/src/Transformer/Contracts/TransformerInterface.php b/src/Transformer/Contracts/TransformerInterface.php
index 79af606..08f37ac 100644
--- a/src/Transformer/Contracts/TransformerInterface.php
+++ b/src/Transformer/Contracts/TransformerInterface.php
@@ -13,10 +13,10 @@
 
 namespace Rekalogika\Mapper\Transformer\Contracts;
 
-use Rekalogika\Mapper\Exception\CircularReferenceException;
 use Rekalogika\Mapper\Exception\ExceptionInterface;
 use Rekalogika\Mapper\Exception\InvalidArgumentException;
 use Rekalogika\Mapper\Exception\LogicException;
+use Rekalogika\Mapper\ObjectCache\Exception\CircularReferenceException;
 use Symfony\Component\PropertyInfo\Type;
 
 interface TransformerInterface
diff --git a/src/Exception/ClassNotInstantiableException.php b/src/Transformer/Exception/ClassNotInstantiableException.php
similarity index 91%
rename from src/Exception/ClassNotInstantiableException.php
rename to src/Transformer/Exception/ClassNotInstantiableException.php
index f87500f..1cc6b1a 100644
--- a/src/Exception/ClassNotInstantiableException.php
+++ b/src/Transformer/Exception/ClassNotInstantiableException.php
@@ -11,7 +11,7 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\Transformer\Exception;
 
 class ClassNotInstantiableException extends NotMappableValueException
 {
diff --git a/src/Exception/IncompleteConstructorArgument.php b/src/Transformer/Exception/IncompleteConstructorArgument.php
similarity index 94%
rename from src/Exception/IncompleteConstructorArgument.php
rename to src/Transformer/Exception/IncompleteConstructorArgument.php
index f827f90..4bf6262 100644
--- a/src/Exception/IncompleteConstructorArgument.php
+++ b/src/Transformer/Exception/IncompleteConstructorArgument.php
@@ -11,7 +11,7 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\Transformer\Exception;
 
 class IncompleteConstructorArgument extends NotMappableValueException
 {
diff --git a/src/Exception/InstantiationFailureException.php b/src/Transformer/Exception/InstantiationFailureException.php
similarity index 97%
rename from src/Exception/InstantiationFailureException.php
rename to src/Transformer/Exception/InstantiationFailureException.php
index 61e619d..81acbdb 100644
--- a/src/Exception/InstantiationFailureException.php
+++ b/src/Transformer/Exception/InstantiationFailureException.php
@@ -11,7 +11,7 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\Transformer\Exception;
 
 class InstantiationFailureException extends NotMappableValueException
 {
diff --git a/src/Exception/InvalidClassException.php b/src/Transformer/Exception/InvalidClassException.php
similarity index 85%
rename from src/Exception/InvalidClassException.php
rename to src/Transformer/Exception/InvalidClassException.php
index dd27f24..f024a84 100644
--- a/src/Exception/InvalidClassException.php
+++ b/src/Transformer/Exception/InvalidClassException.php
@@ -11,8 +11,9 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\Transformer\Exception;
 
+use Rekalogika\Mapper\Exception\UnexpectedValueException;
 use Rekalogika\Mapper\Util\TypeUtil;
 use Symfony\Component\PropertyInfo\Type;
 
diff --git a/src/Exception/InvalidTypeInArgumentException.php b/src/Transformer/Exception/InvalidTypeInArgumentException.php
similarity index 84%
rename from src/Exception/InvalidTypeInArgumentException.php
rename to src/Transformer/Exception/InvalidTypeInArgumentException.php
index a8778d6..3b728dd 100644
--- a/src/Exception/InvalidTypeInArgumentException.php
+++ b/src/Transformer/Exception/InvalidTypeInArgumentException.php
@@ -11,8 +11,9 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\Transformer\Exception;
 
+use Rekalogika\Mapper\Exception\InvalidArgumentException;
 use Rekalogika\Mapper\Util\TypeUtil;
 use Symfony\Component\PropertyInfo\Type;
 
diff --git a/src/Exception/MissingMemberKeyTypeException.php b/src/Transformer/Exception/MissingMemberKeyTypeException.php
similarity index 95%
rename from src/Exception/MissingMemberKeyTypeException.php
rename to src/Transformer/Exception/MissingMemberKeyTypeException.php
index 3fe22e1..5e41b06 100644
--- a/src/Exception/MissingMemberKeyTypeException.php
+++ b/src/Transformer/Exception/MissingMemberKeyTypeException.php
@@ -11,7 +11,7 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\Transformer\Exception;
 
 use Rekalogika\Mapper\Transformer\Contracts\MixedType;
 use Rekalogika\Mapper\Util\TypeUtil;
diff --git a/src/Exception/MissingMemberTypeException.php b/src/Transformer/Exception/MissingMemberTypeException.php
similarity index 87%
rename from src/Exception/MissingMemberTypeException.php
rename to src/Transformer/Exception/MissingMemberTypeException.php
index 91c92bb..0b94e5b 100644
--- a/src/Exception/MissingMemberTypeException.php
+++ b/src/Transformer/Exception/MissingMemberTypeException.php
@@ -11,7 +11,7 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\Transformer\Exception;
 
 abstract class MissingMemberTypeException extends NotMappableValueException
 {
diff --git a/src/Exception/MissingMemberValueTypeException.php b/src/Transformer/Exception/MissingMemberValueTypeException.php
similarity index 95%
rename from src/Exception/MissingMemberValueTypeException.php
rename to src/Transformer/Exception/MissingMemberValueTypeException.php
index 75b633d..0a2172b 100644
--- a/src/Exception/MissingMemberValueTypeException.php
+++ b/src/Transformer/Exception/MissingMemberValueTypeException.php
@@ -11,7 +11,7 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\Transformer\Exception;
 
 use Rekalogika\Mapper\Transformer\Contracts\MixedType;
 use Rekalogika\Mapper\Util\TypeUtil;
diff --git a/src/Exception/NotMappableValueException.php b/src/Transformer/Exception/NotMappableValueException.php
similarity index 76%
rename from src/Exception/NotMappableValueException.php
rename to src/Transformer/Exception/NotMappableValueException.php
index 1552e2b..71064c8 100644
--- a/src/Exception/NotMappableValueException.php
+++ b/src/Transformer/Exception/NotMappableValueException.php
@@ -11,7 +11,9 @@
  * that was distributed with this source code.
  */
 
-namespace Rekalogika\Mapper\Exception;
+namespace Rekalogika\Mapper\Transformer\Exception;
+
+use Rekalogika\Mapper\Exception\UnexpectedValueException;
 
 abstract class NotMappableValueException extends UnexpectedValueException
 {
diff --git a/src/Transformer/ObjectToObjectTransformer.php b/src/Transformer/ObjectToObjectTransformer.php
index 01436bc..a418a4f 100644
--- a/src/Transformer/ObjectToObjectTransformer.php
+++ b/src/Transformer/ObjectToObjectTransformer.php
@@ -13,18 +13,18 @@
 
 namespace Rekalogika\Mapper\Transformer;
 
-use Rekalogika\Mapper\Exception\CachedTargetObjectNotFoundException;
-use Rekalogika\Mapper\Exception\ClassNotInstantiableException;
-use Rekalogika\Mapper\Exception\IncompleteConstructorArgument;
-use Rekalogika\Mapper\Exception\InstantiationFailureException;
 use Rekalogika\Mapper\Exception\InvalidArgumentException;
-use Rekalogika\Mapper\Exception\InvalidClassException;
 use Rekalogika\Mapper\MainTransformer\MainTransformer;
+use Rekalogika\Mapper\ObjectCache\Exception\CachedTargetObjectNotFoundException;
 use Rekalogika\Mapper\ObjectCache\ObjectCacheFactoryInterface;
 use Rekalogika\Mapper\Transformer\Contracts\MainTransformerAwareInterface;
 use Rekalogika\Mapper\Transformer\Contracts\MainTransformerAwareTrait;
 use Rekalogika\Mapper\Transformer\Contracts\TransformerInterface;
 use Rekalogika\Mapper\Transformer\Contracts\TypeMapping;
+use Rekalogika\Mapper\Transformer\Exception\ClassNotInstantiableException;
+use Rekalogika\Mapper\Transformer\Exception\IncompleteConstructorArgument;
+use Rekalogika\Mapper\Transformer\Exception\InstantiationFailureException;
+use Rekalogika\Mapper\Transformer\Exception\InvalidClassException;
 use Rekalogika\Mapper\TypeResolver\TypeResolverInterface;
 use Rekalogika\Mapper\Util\TypeCheck;
 use Rekalogika\Mapper\Util\TypeFactory;
diff --git a/src/Transformer/StringToBackedEnumTransformer.php b/src/Transformer/StringToBackedEnumTransformer.php
index f8f37ea..2bba1de 100644
--- a/src/Transformer/StringToBackedEnumTransformer.php
+++ b/src/Transformer/StringToBackedEnumTransformer.php
@@ -16,6 +16,7 @@
 use Rekalogika\Mapper\Exception\InvalidArgumentException;
 use Rekalogika\Mapper\Transformer\Contracts\TransformerInterface;
 use Rekalogika\Mapper\Transformer\Contracts\TypeMapping;
+use Rekalogika\Mapper\Transformer\Exception\InvalidTypeInArgumentException;
 use Rekalogika\Mapper\Util\TypeFactory;
 use Symfony\Component\PropertyInfo\Type;
 
@@ -35,7 +36,7 @@ public function transform(
         $class = $targetType?->getClassName();
 
         if ($class === null || !\enum_exists($class)) {
-            throw new InvalidArgumentException(sprintf('Target must be an enum class-string, "%s" given', get_debug_type($class)));
+            throw new InvalidTypeInArgumentException('Target must be an enum class-string, "%s" given', $targetType);
         }
 
         // @todo maybe add option to handle values not in the enum
diff --git a/src/Transformer/TraversableToArrayAccessTransformer.php b/src/Transformer/TraversableToArrayAccessTransformer.php
index 1072f35..3726919 100644
--- a/src/Transformer/TraversableToArrayAccessTransformer.php
+++ b/src/Transformer/TraversableToArrayAccessTransformer.php
@@ -15,16 +15,17 @@
 
 use Doctrine\Common\Collections\ArrayCollection;
 use Doctrine\Common\Collections\Collection;
-use Rekalogika\Mapper\Exception\CachedTargetObjectNotFoundException;
 use Rekalogika\Mapper\Exception\InvalidArgumentException;
-use Rekalogika\Mapper\Exception\InvalidTypeInArgumentException;
-use Rekalogika\Mapper\Exception\MissingMemberKeyTypeException;
 use Rekalogika\Mapper\MainTransformer\MainTransformer;
+use Rekalogika\Mapper\ObjectCache\Exception\CachedTargetObjectNotFoundException;
 use Rekalogika\Mapper\ObjectCache\ObjectCacheFactoryInterface;
 use Rekalogika\Mapper\Transformer\Contracts\MainTransformerAwareInterface;
 use Rekalogika\Mapper\Transformer\Contracts\MainTransformerAwareTrait;
 use Rekalogika\Mapper\Transformer\Contracts\TransformerInterface;
 use Rekalogika\Mapper\Transformer\Contracts\TypeMapping;
+use Rekalogika\Mapper\Transformer\Exception\ClassNotInstantiableException;
+use Rekalogika\Mapper\Transformer\Exception\InvalidTypeInArgumentException;
+use Rekalogika\Mapper\Transformer\Exception\MissingMemberKeyTypeException;
 use Rekalogika\Mapper\Util\TypeCheck;
 use Rekalogika\Mapper\Util\TypeFactory;
 use Symfony\Component\PropertyInfo\Type;
@@ -193,7 +194,7 @@ private function instantiateArrayAccessOrArray(
             try {
                 $result = $reflectionClass->newInstance();
             } catch (\ReflectionException) {
-                throw new InvalidArgumentException(sprintf('We do not know how to instantiate class "%s"', $class));
+                throw new ClassNotInstantiableException($class);
             }
 
             if (!$result instanceof \ArrayAccess) {
diff --git a/src/Transformer/TraversableToTraversableTransformer.php b/src/Transformer/TraversableToTraversableTransformer.php
index 0010c0b..370db40 100644
--- a/src/Transformer/TraversableToTraversableTransformer.php
+++ b/src/Transformer/TraversableToTraversableTransformer.php
@@ -13,16 +13,16 @@
 
 namespace Rekalogika\Mapper\Transformer;
 
-use Rekalogika\Mapper\Exception\CachedTargetObjectNotFoundException;
 use Rekalogika\Mapper\Exception\InvalidArgumentException;
-use Rekalogika\Mapper\Exception\MissingMemberKeyTypeException;
-use Rekalogika\Mapper\Exception\MissingMemberValueTypeException;
 use Rekalogika\Mapper\MainTransformer\MainTransformer;
+use Rekalogika\Mapper\ObjectCache\Exception\CachedTargetObjectNotFoundException;
 use Rekalogika\Mapper\ObjectCache\ObjectCacheFactoryInterface;
 use Rekalogika\Mapper\Transformer\Contracts\MainTransformerAwareInterface;
 use Rekalogika\Mapper\Transformer\Contracts\MainTransformerAwareTrait;
 use Rekalogika\Mapper\Transformer\Contracts\TransformerInterface;
 use Rekalogika\Mapper\Transformer\Contracts\TypeMapping;
+use Rekalogika\Mapper\Transformer\Exception\MissingMemberKeyTypeException;
+use Rekalogika\Mapper\Transformer\Exception\MissingMemberValueTypeException;
 use Rekalogika\Mapper\Transformer\Model\TraversableCountableWrapper;
 use Rekalogika\Mapper\Util\TypeCheck;
 use Rekalogika\Mapper\Util\TypeFactory;
diff --git a/src/Util/TypeCheck.php b/src/Util/TypeCheck.php
index 11efb61..49ef7de 100644
--- a/src/Util/TypeCheck.php
+++ b/src/Util/TypeCheck.php
@@ -112,9 +112,26 @@ public static function isEnum(?Type $type): bool
         if ($type === null) {
             return false;
         }
+
+        $class = $type->getClassName();
+
         return $type->getBuiltinType() === Type::BUILTIN_TYPE_OBJECT
-            && $type->getClassName() !== null
-            && enum_exists($type->getClassName());
+            && $class !== null
+            && enum_exists($class);
+    }
+
+    public static function isBackedEnum(?Type $type): bool
+    {
+        if ($type === null) {
+            return false;
+        }
+
+        $class = $type->getClassName();
+
+        return $type->getBuiltinType() === Type::BUILTIN_TYPE_OBJECT
+            && $class !== null
+            && enum_exists($class)
+            && is_a($class, \BackedEnum::class, true);
     }
 
     public static function isResource(?Type $type): bool
@@ -212,8 +229,12 @@ public static function isTypeInstanceOf(
     /**
      * @todo support generics
      */
-    public static function isVariableInstanceOf(mixed $variable, Type $type): bool
+    public static function isVariableInstanceOf(mixed $variable, Type|MixedType $type): bool
     {
+        if ($type instanceof MixedType) {
+            return true;
+        }
+
         if (self::isObject($type)) {
             $class = $type->getClassName();
 
diff --git a/src/Util/TypeUtil.php b/src/Util/TypeUtil.php
index bff2751..493bf0f 100644
--- a/src/Util/TypeUtil.php
+++ b/src/Util/TypeUtil.php
@@ -14,9 +14,8 @@
 namespace Rekalogika\Mapper\Util;
 
 use DaveLiddament\PhpLanguageExtensions\Friend;
-use DaveLiddament\PhpLanguageExtensions\NamespaceVisibility;
 use Rekalogika\Mapper\Exception\InvalidArgumentException;
-use Rekalogika\Mapper\Exception\MapperReturnsUnexpectedValueException;
+use Rekalogika\Mapper\MainTransformer\Exception\TransformerReturnsUnexpectedValueException;
 use Rekalogika\Mapper\Tests\UnitTest\Util\TypeUtil2Test;
 use Rekalogika\Mapper\Tests\UnitTest\Util\TypeUtilTest;
 use Rekalogika\Mapper\Transformer\Contracts\MixedType;
@@ -231,7 +230,6 @@ class: $type->getClassName(),
      * @param null|Type|MixedType|array<array-key,Type|MixedType> $type
      * @return string
      */
-    #[NamespaceVisibility(namespace: 'Rekalogika\Mapper\Exception')]
     public static function getDebugType(null|Type|MixedType|array $type): string
     {
         if ($type === null) {
@@ -260,7 +258,7 @@ public static function getDebugType(null|Type|MixedType|array $type): string
      */
     #[Friend(
         TypeResolver::class,
-        MapperReturnsUnexpectedValueException::class,
+        TransformerReturnsUnexpectedValueException::class,
         TypeUtilTest::class
     )]
     public static function getTypeString(Type|MixedType $type): string
diff --git a/tests/IntegrationTest/ConstructorTest.php b/tests/IntegrationTest/ConstructorTest.php
index 2d1b538..b7afd2a 100644
--- a/tests/IntegrationTest/ConstructorTest.php
+++ b/tests/IntegrationTest/ConstructorTest.php
@@ -13,9 +13,6 @@
 
 namespace Rekalogika\Mapper\Tests\IntegrationTest;
 
-use Rekalogika\Mapper\Exception\ClassNotInstantiableException;
-use Rekalogika\Mapper\Exception\IncompleteConstructorArgument;
-use Rekalogika\Mapper\Exception\InstantiationFailureException;
 use Rekalogika\Mapper\Tests\Common\AbstractIntegrationTest;
 use Rekalogika\Mapper\Tests\Fixtures\Constructor\ObjectWithConstructorAndMoreArgumentDto;
 use Rekalogika\Mapper\Tests\Fixtures\Constructor\ObjectWithConstructorAndPropertiesDto;
@@ -23,6 +20,9 @@
 use Rekalogika\Mapper\Tests\Fixtures\Constructor\ObjectWithPrivateConstructorDto;
 use Rekalogika\Mapper\Tests\Fixtures\Scalar\ObjectWithScalarProperties;
 use Rekalogika\Mapper\Tests\Fixtures\Scalar\ObjectWithScalarPropertiesAndAdditionalNullProperty;
+use Rekalogika\Mapper\Transformer\Exception\ClassNotInstantiableException;
+use Rekalogika\Mapper\Transformer\Exception\IncompleteConstructorArgument;
+use Rekalogika\Mapper\Transformer\Exception\InstantiationFailureException;
 
 class ConstructorTest extends AbstractIntegrationTest
 {
diff --git a/tests/UnitTest/Model/ObjectCacheTest.php b/tests/UnitTest/Model/ObjectCacheTest.php
index c57f911..6c67198 100644
--- a/tests/UnitTest/Model/ObjectCacheTest.php
+++ b/tests/UnitTest/Model/ObjectCacheTest.php
@@ -34,7 +34,7 @@ public function testObjectCache(): void
         $this->assertTrue($objectCache->containsTarget($source, TypeFactory::int()));
         $this->assertSame($target, $objectCache->getTarget($source, TypeFactory::int()));
 
-        $this->expectException(\Rekalogika\Mapper\Exception\CachedTargetObjectNotFoundException::class);
+        $this->expectException(\Rekalogika\Mapper\ObjectCache\Exception\CachedTargetObjectNotFoundException::class);
         $objectCache->getTarget($source, TypeFactory::float());
     }
 }