diff --git a/lib/Doctrine/ORM/Persisters/BasicEntityPersister.php b/lib/Doctrine/ORM/Persisters/BasicEntityPersister.php
index 176eb38f8..8d2aa5236 100644
--- a/lib/Doctrine/ORM/Persisters/BasicEntityPersister.php
+++ b/lib/Doctrine/ORM/Persisters/BasicEntityPersister.php
@@ -1848,16 +1848,7 @@ class BasicEntityPersister
             return $value;
         }
 
-        if ($this->em->getUnitOfWork()->getEntityState($value) === UnitOfWork::STATE_MANAGED) {
-            $idValues = $this->em->getUnitOfWork()->getEntityIdentifier($value);
-
-            return reset($idValues);
-        }
-
-        $class      = $this->em->getClassMetadata(get_class($value));
-        $idValues   = $class->getIdentifierValues($value);
-
-        return reset($idValues);
+        return $this->em->getUnitOfWork()->getSingleIdentifierValue($value);
     }
 
     /**
diff --git a/lib/Doctrine/ORM/UnitOfWork.php b/lib/Doctrine/ORM/UnitOfWork.php
index c1065dba2..498c4a699 100644
--- a/lib/Doctrine/ORM/UnitOfWork.php
+++ b/lib/Doctrine/ORM/UnitOfWork.php
@@ -2860,7 +2860,7 @@ class UnitOfWork implements PropertyChangedListener
             throw ORMInvalidArgumentException::invalidCompositeIdentifier();
         }
 
-        $values = ($this->getEntityState($entity) === UnitOfWork::STATE_MANAGED)
+        $values = $this->isInIdentityMap($entity)
             ? $this->getEntityIdentifier($entity)
             : $class->getIdentifierValues($entity);
 
diff --git a/tests/Doctrine/Tests/ORM/Functional/Ticket/DDC2106Test.php b/tests/Doctrine/Tests/ORM/Functional/Ticket/DDC2106Test.php
new file mode 100644
index 000000000..0de386f9a
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/Ticket/DDC2106Test.php
@@ -0,0 +1,64 @@
+<?php
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\Tests\Models\Generic\DateTimeModel;
+use Doctrine\Common\Collections\Criteria;
+
+/**
+ * @group DDC-2106
+ */
+class DDC2106Test extends \Doctrine\Tests\OrmFunctionalTestCase
+{
+    protected function setUp()
+    {
+        parent::setUp();
+        $this->_schemaTool->createSchema(array(
+            $this->_em->getClassMetadata(__NAMESPACE__ . '\DDC2106Entity'),
+        ));
+    }
+
+    public function testDetachedEntityAsId()
+    {
+        // We want an uninitialized PersistentCollection $entity->children
+        $entity = new DDC2106Entity();
+        $this->_em->persist($entity);
+        $this->_em->flush();
+        $this->_em->detach($entity);
+        $entity = $this->_em->getRepository(__NAMESPACE__ . '\DDC2106Entity')->findOneBy(array());
+
+        // ... and a managed entity without id
+        $entityWithoutId = new DDC2106Entity();
+        $this->_em->persist($entityWithoutId);
+
+        $criteria = Criteria::create()->where(Criteria::expr()->eq('parent', $entityWithoutId));
+        $entity->children->matching($criteria)->count();
+    }
+}
+
+/**
+ * @Entity
+ */
+class DDC2106Entity
+{
+    /**
+     * @Id
+     * @GeneratedValue(strategy="IDENTITY")
+     * @Column(type="integer")
+     */
+    public $id;
+
+    /** @ManyToOne(targetEntity="DDC2106Entity", inversedBy="children") */
+    public $parent;
+
+    /**
+     * @OneToMany(targetEntity="DDC2106Entity", mappedBy="parent", cascade={"persist"})
+     */
+    public $children;
+
+    public function __construct()
+    {
+        $this->children = new \Doctrine\Common\Collections\ArrayCollection;
+    }
+}
+