diff --git a/src/Drupal/DrupalAutoloader.php b/src/Drupal/DrupalAutoloader.php
index 9b681dd5..b1ef6546 100644
--- a/src/Drupal/DrupalAutoloader.php
+++ b/src/Drupal/DrupalAutoloader.php
@@ -188,13 +188,6 @@ public function register(Container $container): void
                 continue;
             }
             foreach ($yaml['services'] as $serviceId => $serviceDefinition) {
-                // Check if this is an alias shortcut.
-                // @link https://symfony.com/doc/4.4/service_container/alias_private.html#aliasing
-                if (is_string($serviceDefinition)) {
-                    $serviceDefinition = [
-                        'alias' => str_replace('@', '', $serviceDefinition),
-                    ];
-                }
                 // Prevent \Nette\DI\ContainerBuilder::completeStatement from array_walk_recursive into the arguments
                 // and thinking these are real services for PHPStan's container.
                 if (isset($serviceDefinition['arguments']) && is_array($serviceDefinition['arguments'])) {
diff --git a/src/Drupal/ServiceMap.php b/src/Drupal/ServiceMap.php
index b27c5e4b..10ca68f7 100644
--- a/src/Drupal/ServiceMap.php
+++ b/src/Drupal/ServiceMap.php
@@ -28,6 +28,21 @@ public function setDrupalServices(array $drupalServices): void
         $decorators = [];
 
         foreach ($drupalServices as $serviceId => $serviceDefinition) {
+            // @todo this duplicates \Symfony\Component\DependencyInjection\Loader\YamlFileLoader::parseDefinition()
+            //   Can we re-use the YamlFileLoader instead of this manual parsing?
+            if (is_string($serviceDefinition) && strpos($serviceDefinition, '@') === 0) {
+                $serviceDefinition = [
+                    'alias' => substr($serviceDefinition, 1)
+                ];
+            }
+            if (is_null($serviceDefinition)) {
+                $serviceDefinition = [];
+            }
+
+            if (!is_array($serviceDefinition)) {
+                continue;
+            }
+
             if (isset($serviceDefinition['alias'], $drupalServices[$serviceDefinition['alias']])) {
                 $serviceDefinition = $drupalServices[$serviceDefinition['alias']];
             }
@@ -40,6 +55,10 @@ public function setDrupalServices(array $drupalServices): void
             }
 
             // @todo support factories
+            if (isset($serviceDefinition['factory'])) {
+                continue;
+            }
+
             if (!isset($serviceDefinition['class'])) {
                 if (class_exists($serviceId)) {
                     $serviceDefinition['class'] = $serviceId;
@@ -60,11 +79,14 @@ public function setDrupalServices(array $drupalServices): void
         }
 
         foreach ($decorators as $decorated_service_id => $services) {
-            foreach ($services as $dcorating_service_id) {
-                if (!isset(self::$services[$decorated_service_id])) {
+            if (!isset(self::$services[$decorated_service_id])) {
+                continue;
+            }
+            foreach ($services as $decorating_service_id) {
+                if (!isset(self::$services[$decorating_service_id])) {
                     continue;
                 }
-                self::$services[$decorated_service_id]->addDecorator(self::$services[$dcorating_service_id]);
+                self::$services[$decorated_service_id]->addDecorator(self::$services[$decorating_service_id]);
             }
         }
     }
@@ -73,7 +95,7 @@ private function resolveParentDefinition(string $parentId, array $serviceDefinit
     {
         $parentDefinition = $drupalServices[$parentId] ?? [];
         if ([] === $parentDefinition) {
-            return $serviceDefinition;
+            return $parentDefinition;
         }
 
         if (isset($parentDefinition['parent'])) {
diff --git a/tests/fixtures/drupal/modules/phpstan_fixtures/phpstan_fixtures.services.yml b/tests/fixtures/drupal/modules/phpstan_fixtures/phpstan_fixtures.services.yml
new file mode 100644
index 00000000..f036e072
--- /dev/null
+++ b/tests/fixtures/drupal/modules/phpstan_fixtures/phpstan_fixtures.services.yml
@@ -0,0 +1,8 @@
+services:
+  _defaults:
+    autowire: true
+
+  Drupal\phpstan_fixtures\Foo:
+  Drupal\phpstan_fixtures\BarInterface: '@Drupal\phpstan_fixtures\Bar'
+  Drupal\phpstan_fixtures\Bar:
+    decorates: Drupal\phpstan_fixtures\Foo
diff --git a/tests/fixtures/drupal/modules/phpstan_fixtures/src/Bar.php b/tests/fixtures/drupal/modules/phpstan_fixtures/src/Bar.php
new file mode 100644
index 00000000..13214a71
--- /dev/null
+++ b/tests/fixtures/drupal/modules/phpstan_fixtures/src/Bar.php
@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\phpstan_fixtures;
+
+final class Bar implements BarInterface
+{
+
+    public function __construct(Foo $inner)
+    {
+    }
+
+}
diff --git a/tests/fixtures/drupal/modules/phpstan_fixtures/src/BarInterface.php b/tests/fixtures/drupal/modules/phpstan_fixtures/src/BarInterface.php
new file mode 100644
index 00000000..8ec64762
--- /dev/null
+++ b/tests/fixtures/drupal/modules/phpstan_fixtures/src/BarInterface.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Drupal\phpstan_fixtures;
+
+interface  BarInterface
+{
+
+}
diff --git a/tests/fixtures/drupal/modules/phpstan_fixtures/src/Foo.php b/tests/fixtures/drupal/modules/phpstan_fixtures/src/Foo.php
new file mode 100644
index 00000000..837ec065
--- /dev/null
+++ b/tests/fixtures/drupal/modules/phpstan_fixtures/src/Foo.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace Drupal\phpstan_fixtures;
+
+final class Foo {
+
+}
diff --git a/tests/src/ServiceMapFactoryTest.php b/tests/src/ServiceMapFactoryTest.php
index 5834bb9e..dca90d21 100644
--- a/tests/src/ServiceMapFactoryTest.php
+++ b/tests/src/ServiceMapFactoryTest.php
@@ -26,6 +26,8 @@ final class ServiceMapFactoryTest extends TestCase
      */
     public function testFactory(string $id, callable $validator): void
     {
+        require_once __DIR__ . '/data/bug-693.php';
+
         $service = new ServiceMap();
         $service->setDrupalServices([
             'entity_type.manager' => [
@@ -112,6 +114,11 @@ public function testFactory(string $id, callable $validator): void
                 'decorates' => 'unknown',
                 'class' => 'Drupal\service_map\Override',
             ],
+            'Bug693\Foo' => null,
+            'Bug693\BarInterface' => '@Bug693\Bar',
+            'Bug693\Bar' => [
+                'decorates' => 'Bug693\Foo'
+            ],
         ]);
         $validator($service->getService($id));
     }
@@ -241,6 +248,13 @@ function (DrupalServiceDefinition $service): void {
                 self::assertArrayHasKey('service_map.decorates_decorating_base', $child_decorators);
             }
         ];
+        yield [
+            'Bug693\Foo',
+            function (DrupalServiceDefinition $service): void {
+                self::assertCount(1, $service->getDecorators());
+                self::assertArrayHasKey('Bug693\\Bar', $service->getDecorators());
+            }
+        ];
     }
 
 }
diff --git a/tests/src/data/bug-693.php b/tests/src/data/bug-693.php
new file mode 100644
index 00000000..8b978edc
--- /dev/null
+++ b/tests/src/data/bug-693.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace Bug693;
+
+final class Foo
+{
+
+}
+
+interface BarInterface
+{
+
+}
+
+final class Bar implements BarInterface
+{
+
+}