diff --git a/src/CommandBus/Handler/CreateAggregateHandler.php b/src/CommandBus/Handler/CreateAggregateHandler.php
index ae319abdb..82e6e839b 100644
--- a/src/CommandBus/Handler/CreateAggregateHandler.php
+++ b/src/CommandBus/Handler/CreateAggregateHandler.php
@@ -7,7 +7,6 @@
 use InvalidArgumentException;
 use Patchlevel\EventSourcing\Aggregate\AggregateRoot;
 use Patchlevel\EventSourcing\Repository\RepositoryManager;
-use Psr\Container\ContainerInterface;
 use ReflectionClass;
 
 final class CreateAggregateHandler
@@ -17,7 +16,7 @@ public function __construct(
         private readonly RepositoryManager $repositoryManager,
         private readonly string $aggregateClass,
         private readonly string $methodName,
-        private readonly ContainerInterface|null $container = null,
+        private readonly ParameterResolver $parameterResolver,
     ) {
     }
 
@@ -30,10 +29,7 @@ public function __invoke(object $command): void
 
         $aggregate = $reflectionMethod->invokeArgs(
             null,
-            [
-                $command,
-                ...ParameterResolver::resolve($reflectionMethod, $this->container),
-            ],
+            [...$this->parameterResolver->resolve($reflectionMethod, $command)],
         );
 
         if (!$aggregate instanceof AggregateRoot) {
diff --git a/src/CommandBus/Handler/DefaultHandlerFactory.php b/src/CommandBus/Handler/DefaultHandlerFactory.php
index 853047632..b371c8325 100644
--- a/src/CommandBus/Handler/DefaultHandlerFactory.php
+++ b/src/CommandBus/Handler/DefaultHandlerFactory.php
@@ -21,7 +21,7 @@ public function createHandler(string $aggregateClass, string $method): callable
             $this->repositoryManager,
             $aggregateClass,
             $method,
-            $this->container,
+            new DefaultParameterResolver($this->container),
         );
     }
 
@@ -31,7 +31,7 @@ public function updateHandler(string $aggregateClass, string $method): callable
             $this->repositoryManager,
             $aggregateClass,
             $method,
-            $this->container,
+            new DefaultParameterResolver($this->container),
         );
     }
 }
diff --git a/src/CommandBus/Handler/DefaultParameterResolver.php b/src/CommandBus/Handler/DefaultParameterResolver.php
new file mode 100644
index 000000000..da11882d2
--- /dev/null
+++ b/src/CommandBus/Handler/DefaultParameterResolver.php
@@ -0,0 +1,61 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\EventSourcing\CommandBus\Handler;
+
+use Patchlevel\EventSourcing\Attribute\Inject;
+use Psr\Container\ContainerInterface;
+use ReflectionMethod;
+use ReflectionParameter;
+use Symfony\Component\TypeInfo\Type\ObjectType;
+use Symfony\Component\TypeInfo\TypeResolver\TypeResolver;
+
+final class DefaultParameterResolver implements ParameterResolver
+{
+    public function __construct(
+        private readonly ContainerInterface|null $container = null,
+    ) {
+    }
+
+    /** @return iterable<mixed> */
+    public function resolve(ReflectionMethod $method, object $command): iterable
+    {
+        foreach ($method->getParameters() as $index => $parameter) {
+            if ($index === 0) {
+                yield $command; // first parameter is always the command
+
+                continue;
+            }
+
+            if (!$this->container) {
+                throw ServiceNotResolvable::missingContainer();
+            }
+
+            yield $this->container->get(self::serviceName($method, $parameter));
+        }
+    }
+
+    private function serviceName(ReflectionMethod $method, ReflectionParameter $parameter): string
+    {
+        $attributes = $parameter->getAttributes(Inject::class);
+
+        if ($attributes !== []) {
+            return $attributes[0]->newInstance()->service;
+        }
+
+        $reflectionType = $parameter->getType();
+
+        if ($reflectionType === null) {
+            throw ServiceNotResolvable::missingType($method->getDeclaringClass()->getName(), $parameter->getName());
+        }
+
+        $type = TypeResolver::create()->resolve($reflectionType);
+
+        if (!$type instanceof ObjectType) {
+            throw ServiceNotResolvable::typeNotObject($method->getDeclaringClass()->getName(), $parameter->getName());
+        }
+
+        return $type->getClassName();
+    }
+}
diff --git a/src/CommandBus/Handler/ParameterResolver.php b/src/CommandBus/Handler/ParameterResolver.php
index 69238e9ed..53145a801 100644
--- a/src/CommandBus/Handler/ParameterResolver.php
+++ b/src/CommandBus/Handler/ParameterResolver.php
@@ -4,52 +4,10 @@
 
 namespace Patchlevel\EventSourcing\CommandBus\Handler;
 
-use Patchlevel\EventSourcing\Attribute\Inject;
-use Psr\Container\ContainerInterface;
 use ReflectionMethod;
-use ReflectionParameter;
-use Symfony\Component\TypeInfo\Type\ObjectType;
-use Symfony\Component\TypeInfo\TypeResolver\TypeResolver;
 
-/** @internal */
-final class ParameterResolver
+interface ParameterResolver
 {
     /** @return iterable<mixed> */
-    public static function resolve(ReflectionMethod $method, ContainerInterface|null $container = null): iterable
-    {
-        foreach ($method->getParameters() as $index => $parameter) {
-            if ($index === 0) {
-                continue; // skip first parameter (command)
-            }
-
-            if (!$container) {
-                throw ServiceNotResolvable::missingContainer();
-            }
-
-            yield $container->get(self::serviceName($method, $parameter));
-        }
-    }
-
-    private static function serviceName(ReflectionMethod $method, ReflectionParameter $parameter): string
-    {
-        $attributes = $parameter->getAttributes(Inject::class);
-
-        if ($attributes !== []) {
-            return $attributes[0]->newInstance()->service;
-        }
-
-        $reflectionType = $parameter->getType();
-
-        if ($reflectionType === null) {
-            throw ServiceNotResolvable::missingType($method->getDeclaringClass()->getName(), $parameter->getName());
-        }
-
-        $type = TypeResolver::create()->resolve($reflectionType);
-
-        if (!$type instanceof ObjectType) {
-            throw ServiceNotResolvable::typeNotObject($method->getDeclaringClass()->getName(), $parameter->getName());
-        }
-
-        return $type->getClassName();
-    }
+    public function resolve(ReflectionMethod $method, object $command): iterable;
 }
diff --git a/src/CommandBus/Handler/UpdateAggregateHandler.php b/src/CommandBus/Handler/UpdateAggregateHandler.php
index bb640f779..b3adfb8c5 100644
--- a/src/CommandBus/Handler/UpdateAggregateHandler.php
+++ b/src/CommandBus/Handler/UpdateAggregateHandler.php
@@ -9,7 +9,6 @@
 use Patchlevel\EventSourcing\Aggregate\AggregateRootId;
 use Patchlevel\EventSourcing\Attribute\Id;
 use Patchlevel\EventSourcing\Repository\RepositoryManager;
-use Psr\Container\ContainerInterface;
 use ReflectionClass;
 
 final class UpdateAggregateHandler
@@ -19,7 +18,7 @@ public function __construct(
         private readonly RepositoryManager $repositoryManager,
         private readonly string $aggregateClass,
         private readonly string $methodName,
-        private readonly ContainerInterface|null $container = null,
+        private readonly ParameterResolver $parameterResolver,
     ) {
     }
 
@@ -35,10 +34,7 @@ public function __invoke(object $command): void
 
         $reflectionMethod->invokeArgs(
             $aggregate,
-            [
-                $command,
-                ...ParameterResolver::resolve($reflectionMethod, $this->container),
-            ],
+            [...$this->parameterResolver->resolve($reflectionMethod, $command)],
         );
 
         $repository->save($aggregate);