diff --git a/src/Drupal/ServiceMap.php b/src/Drupal/ServiceMap.php
index 6809e424..c6368d60 100644
--- a/src/Drupal/ServiceMap.php
+++ b/src/Drupal/ServiceMap.php
@@ -59,6 +59,9 @@ public function setDrupalServices(array $drupalServices): void
 
         foreach ($decorators as $decorated_service_id => $services) {
             foreach ($services as $dcorating_service_id) {
+                if (!isset(self::$services[$decorated_service_id])) {
+                    continue;
+                }
                 self::$services[$decorated_service_id]->addDecorator(self::$services[$dcorating_service_id]);
             }
         }
diff --git a/tests/src/ServiceMapFactoryTest.php b/tests/src/ServiceMapFactoryTest.php
index 3770a705..5834bb9e 100644
--- a/tests/src/ServiceMapFactoryTest.php
+++ b/tests/src/ServiceMapFactoryTest.php
@@ -108,6 +108,10 @@ public function testFactory(string $id, callable $validator): void
                 'decorates' => 'service_map.deocrating_base',
                 'class' => 'Drupal\service_map\Override',
             ],
+            'decorating_an_unknown_service' => [
+                'decorates' => 'unknown',
+                'class' => 'Drupal\service_map\Override',
+            ],
         ]);
         $validator($service->getService($id));
     }