diff --git a/src/Symfony/Component/Security/Acl/Domain/Acl.php b/src/Symfony/Component/Security/Acl/Domain/Acl.php
index 4a4a2e232b07..a890bbec0343 100644
--- a/src/Symfony/Component/Security/Acl/Domain/Acl.php
+++ b/src/Symfony/Component/Security/Acl/Domain/Acl.php
@@ -311,9 +311,9 @@ public function setEntriesInheriting($boolean)
     /**
      * {@inheritDoc}
      */
-    public function setParentAcl(AclInterface $acl)
+    public function setParentAcl(AclInterface $acl = null)
     {
-        if (null === $acl->getId()) {
+        if (null !== $acl && null === $acl->getId()) {
             throw new \InvalidArgumentException('$acl must have an ID.');
         }
 
diff --git a/src/Symfony/Component/Security/Acl/Model/MutableAclInterface.php b/src/Symfony/Component/Security/Acl/Model/MutableAclInterface.php
index 521d307839e4..a846a9f16182 100644
--- a/src/Symfony/Component/Security/Acl/Model/MutableAclInterface.php
+++ b/src/Symfony/Component/Security/Acl/Model/MutableAclInterface.php
@@ -114,9 +114,10 @@ function setEntriesInheriting($boolean);
     /**
      * Sets the parent ACL
      *
-     * @param AclInterface $acl
+     * @param AclInterface|null $acl
+     * @return void
      */
-    function setParentAcl(AclInterface $acl);
+    function setParentAcl(AclInterface $acl = null);
 
     /**
      * Updates a class-based ACE
diff --git a/tests/Symfony/Tests/Component/Security/Acl/Domain/AclTest.php b/tests/Symfony/Tests/Component/Security/Acl/Domain/AclTest.php
index 762ce7693db1..90f13fb40489 100644
--- a/tests/Symfony/Tests/Component/Security/Acl/Domain/AclTest.php
+++ b/tests/Symfony/Tests/Component/Security/Acl/Domain/AclTest.php
@@ -250,6 +250,9 @@ public function testSetGetParentAcl()
         $this->assertNull($acl->getParentAcl());
         $acl->setParentAcl($parentAcl);
         $this->assertSame($parentAcl, $acl->getParentAcl());
+
+        $acl->setParentAcl(null);
+        $this->assertNull($acl->getParentAcl());
     }
 
     public function testSetIsEntriesInheriting()