diff --git a/src/Attribute/Inject.php b/src/Attribute/Inject.php
index 7f2d36ff..bd7a42f7 100644
--- a/src/Attribute/Inject.php
+++ b/src/Attribute/Inject.php
@@ -10,7 +10,7 @@
 final class Inject
 {
     public function __construct(
-        public readonly string|null $service = null,
+        public readonly string $service,
     ) {
     }
 }
diff --git a/src/CommandBus/Handler/ParameterResolver.php b/src/CommandBus/Handler/ParameterResolver.php
index 88ad6166..69238e9e 100644
--- a/src/CommandBus/Handler/ParameterResolver.php
+++ b/src/CommandBus/Handler/ParameterResolver.php
@@ -7,7 +7,7 @@
 use Patchlevel\EventSourcing\Attribute\Inject;
 use Psr\Container\ContainerInterface;
 use ReflectionMethod;
-use RuntimeException;
+use ReflectionParameter;
 use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\TypeInfo\TypeResolver\TypeResolver;
 
@@ -22,35 +22,34 @@ public static function resolve(ReflectionMethod $method, ContainerInterface|null
                 continue; // skip first parameter (command)
             }
 
-            $attributes = $parameter->getAttributes(Inject::class);
-
-            if ($attributes === []) {
-                throw new RuntimeException('missing inject attribute');
+            if (!$container) {
+                throw ServiceNotResolvable::missingContainer();
             }
 
-            $serviceName = $attributes[0]->newInstance()->service;
-
-            if ($serviceName === null) {
-                $reflectionType = $parameter->getType();
+            yield $container->get(self::serviceName($method, $parameter));
+        }
+    }
 
-                if ($reflectionType === null) {
-                    throw new RuntimeException('missing type hint');
-                }
+    private static function serviceName(ReflectionMethod $method, ReflectionParameter $parameter): string
+    {
+        $attributes = $parameter->getAttributes(Inject::class);
 
-                $type = TypeResolver::create()->resolve($reflectionType);
+        if ($attributes !== []) {
+            return $attributes[0]->newInstance()->service;
+        }
 
-                if (!$type instanceof ObjectType) {
-                    throw new RuntimeException('type hint must be object');
-                }
+        $reflectionType = $parameter->getType();
 
-                $serviceName = $type->getClassName();
-            }
+        if ($reflectionType === null) {
+            throw ServiceNotResolvable::missingType($method->getDeclaringClass()->getName(), $parameter->getName());
+        }
 
-            if (!$container) {
-                throw new RuntimeException('missing inject attribute');
-            }
+        $type = TypeResolver::create()->resolve($reflectionType);
 
-            yield $container->get($serviceName);
+        if (!$type instanceof ObjectType) {
+            throw ServiceNotResolvable::typeNotObject($method->getDeclaringClass()->getName(), $parameter->getName());
         }
+
+        return $type->getClassName();
     }
 }
diff --git a/src/CommandBus/Handler/ServiceNotResolvable.php b/src/CommandBus/Handler/ServiceNotResolvable.php
new file mode 100644
index 00000000..44a38281
--- /dev/null
+++ b/src/CommandBus/Handler/ServiceNotResolvable.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace Patchlevel\EventSourcing\CommandBus\Handler;
+
+use RuntimeException;
+
+final class ServiceNotResolvable extends RuntimeException
+{
+    public static function missingType(string $class, $propertyName): self
+    {
+        return new self(sprintf('Missing type for property "%s" in class "%s"', $propertyName, $class));
+    }
+
+    public static function typeNotObject(string $class, $propertyName): self
+    {
+        return new self(sprintf('Type for property "%s" in class "%s" must be object', $propertyName, $class));
+    }
+
+    public static function missingContainer(): self
+    {
+        return new self('Container is not configured');
+    }
+}
\ No newline at end of file
diff --git a/src/CommandBus/ServiceNotFound.php b/src/CommandBus/ServiceNotFound.php
index b9849bd2..ba021f62 100644
--- a/src/CommandBus/ServiceNotFound.php
+++ b/src/CommandBus/ServiceNotFound.php
@@ -13,6 +13,6 @@ final class ServiceNotFound extends RuntimeException implements NotFoundExceptio
 {
     public function __construct(string $id)
     {
-        parent::__construct(sprintf('service %s not found', $id));
+        parent::__construct(sprintf('service "%s" not found', $id));
     }
 }
diff --git a/tests/Integration/BasicImplementation/BasicIntegrationTest.php b/tests/Integration/BasicImplementation/BasicIntegrationTest.php
index 673203c8..e2f8f886 100644
--- a/tests/Integration/BasicImplementation/BasicIntegrationTest.php
+++ b/tests/Integration/BasicImplementation/BasicIntegrationTest.php
@@ -284,6 +284,7 @@ public function testCommandBus(): void
             $manager,
             new ServiceLocator([
                 ClockInterface::class => new SystemClock(),
+                'env' => 'test',
             ]),
         );
 
diff --git a/tests/Integration/BasicImplementation/ProfileWithCommands.php b/tests/Integration/BasicImplementation/ProfileWithCommands.php
index f542c510..da56535d 100644
--- a/tests/Integration/BasicImplementation/ProfileWithCommands.php
+++ b/tests/Integration/BasicImplementation/ProfileWithCommands.php
@@ -28,8 +28,8 @@ final class ProfileWithCommands extends BasicAggregateRoot
     #[Handle]
     public static function create(
         CreateProfile $command,
-        #[Inject]
         ClockInterface $clock,
+        #[Inject('env')] string $env,
     ): self {
         $self = new self();
         $self->recordThat(new ProfileCreated($command->id, $command->name));
@@ -40,8 +40,8 @@ public static function create(
     #[Handle]
     public function changeName(
         ChangeProfileName $command,
-        #[Inject]
         ClockInterface $clock,
+        #[Inject('env')] string $env,
     ): void {
         $this->recordThat(new NameChanged($command->name));
     }