diff --git a/src/Symfony/Component/DependencyInjection/Compiler/ResolveInstanceofConditionalsPass.php b/src/Symfony/Component/DependencyInjection/Compiler/ResolveInstanceofConditionalsPass.php
index a2e62f4e536a..82f13ed2d0e1 100644
--- a/src/Symfony/Component/DependencyInjection/Compiler/ResolveInstanceofConditionalsPass.php
+++ b/src/Symfony/Component/DependencyInjection/Compiler/ResolveInstanceofConditionalsPass.php
@@ -107,6 +107,9 @@ private function processDefinition(ContainerBuilder $container, $id, Definition
             while (0 <= --$i) {
                 foreach ($instanceofTags[$i] as $k => $v) {
                     foreach ($v as $v) {
+                        if ($definition->hasTag($k) && in_array($v, $definition->getTag($k))) {
+                            continue;
+                        }
                         $definition->addTag($k, $v);
                     }
                 }
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Compiler/ResolveInstanceofConditionalsPassTest.php b/src/Symfony/Component/DependencyInjection/Tests/Compiler/ResolveInstanceofConditionalsPassTest.php
index c6c368102560..164ab25941d6 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Compiler/ResolveInstanceofConditionalsPassTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Compiler/ResolveInstanceofConditionalsPassTest.php
@@ -130,6 +130,29 @@ public function testProcessUsesAutoconfiguredInstanceof()
         $this->assertSame(array('local_instanceof_tag' => array(array()), 'autoconfigured_tag' => array(array())), $def->getTags());
     }
 
+    public function testAutoconfigureInstanceofDoesNotDuplicateTags()
+    {
+        $container = new ContainerBuilder();
+        $def = $container->register('normal_service', self::class);
+        $def
+            ->addTag('duplicated_tag')
+            ->addTag('duplicated_tag', array('and_attributes' => 1))
+        ;
+        $def->setInstanceofConditionals(array(
+            parent::class => (new ChildDefinition(''))->addTag('duplicated_tag'),
+        ));
+        $def->setAutoconfigured(true);
+        $container->registerForAutoconfiguration(parent::class)
+            ->addTag('duplicated_tag', array('and_attributes' => 1))
+        ;
+
+        (new ResolveInstanceofConditionalsPass())->process($container);
+        (new ResolveDefinitionTemplatesPass())->process($container);
+
+        $def = $container->getDefinition('normal_service');
+        $this->assertSame(array('duplicated_tag' => array(array(), array('and_attributes' => 1))), $def->getTags());
+    }
+
     public function testProcessDoesNotUseAutoconfiguredInstanceofIfNotEnabled()
     {
         $container = new ContainerBuilder();