diff --git a/lib/Doctrine/ORM/Id/AssignedGenerator.php b/lib/Doctrine/ORM/Id/AssignedGenerator.php
index 3ad2cbff7..447dbd6d5 100644
--- a/lib/Doctrine/ORM/Id/AssignedGenerator.php
+++ b/lib/Doctrine/ORM/Id/AssignedGenerator.php
@@ -40,8 +40,7 @@ class AssignedGenerator extends AbstractIdGenerator
      *
      * @throws \Doctrine\ORM\ORMException
      */
-    public function generate(
-        EntityManager $em, $entity)
+    public function generate(EntityManager $em, $entity)
     {
         $class      = $em->getClassMetadata(get_class($entity));
         $idFields   = $class->getIdentifierFieldNames();
@@ -55,12 +54,8 @@ class AssignedGenerator extends AbstractIdGenerator
             }
 
             if (isset($class->associationMappings[$idField])) {
-                if ( ! $em->getUnitOfWork()->isInIdentityMap($value)) {
-                    throw ORMException::entityMissingForeignAssignedId($entity, $value);
-                }
-
                 // NOTE: Single Columns as associated identifiers only allowed - this constraint it is enforced.
-                $value = current($em->getUnitOfWork()->getEntityIdentifier($value));
+                $value = $em->getUnitOfWork()->getSingleIdentifierValue($value);
             }
 
             $identifier[$idField] = $value;
diff --git a/lib/Doctrine/ORM/Utility/IdentifierFlattener.php b/lib/Doctrine/ORM/Utility/IdentifierFlattener.php
index bb84c6151..166e0acb6 100644
--- a/lib/Doctrine/ORM/Utility/IdentifierFlattener.php
+++ b/lib/Doctrine/ORM/Utility/IdentifierFlattener.php
@@ -36,22 +36,22 @@ final class IdentifierFlattener
     /**
      * The UnitOfWork used to coordinate object-level transactions.
      *
-     * @var \Doctrine\ORM\UnitOfWork
+     * @var UnitOfWork
      */
     private $unitOfWork;
 
     /**
      * The metadata factory, used to retrieve the ORM metadata of entity classes.
      *
-     * @var \Doctrine\Common\Persistence\Mapping\ClassMetadataFactory
+     * @var ClassMetadataFactory
      */
     private $metadataFactory;
 
     /**
      * Initializes a new IdentifierFlattener instance, bound to the given EntityManager.
      *
-     * @param \Doctrine\ORM\UnitOfWork $unitOfWork
-     * @param \Doctrine\Common\Persistence\Mapping\ClassMetadataFactory $metadataFactory
+     * @param UnitOfWork           $unitOfWork
+     * @param ClassMetadataFactory $metadataFactory
      */
     public function __construct(UnitOfWork $unitOfWork, ClassMetadataFactory $metadataFactory)
     {
@@ -62,8 +62,9 @@ final class IdentifierFlattener
     /**
      * convert foreign identifiers into scalar foreign key values to avoid object to string conversion failures.
      *
-     * @param \Doctrine\ORM\Mapping\ClassMetadata $class
-     * @param array $id
+     * @param ClassMetadata $class
+     * @param array         $id
+     *
      * @return array
      */
     public function flattenIdentifier(ClassMetadata $class, array $id)
@@ -72,11 +73,14 @@ final class IdentifierFlattener
 
         foreach ($id as $idField => $idValue) {
             if (isset($class->associationMappings[$idField]) && is_object($idValue)) {
+                /* @var $targetClassMetadata ClassMetadata */
                 $targetClassMetadata = $this->metadataFactory->getMetadataFor(
                     $class->associationMappings[$idField]['targetEntity']
                 );
 
-                $associatedId = $this->unitOfWork->getEntityIdentifier($idValue);
+                $associatedId = $this->unitOfWork->isInIdentityMap($idValue)
+                    ? $this->unitOfWork->getEntityIdentifier($idValue)
+                    : $targetClassMetadata->getIdentifierValues($idValue);
 
                 $flatId[$idField] = $associatedId[$targetClassMetadata->identifier[0]];
             } else {
diff --git a/tests/Doctrine/Tests/Models/MixedToOneIdentity/CompositeToOneKeyState.php b/tests/Doctrine/Tests/Models/MixedToOneIdentity/CompositeToOneKeyState.php
new file mode 100644
index 000000000..b4b02e158
--- /dev/null
+++ b/tests/Doctrine/Tests/Models/MixedToOneIdentity/CompositeToOneKeyState.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace Doctrine\Tests\Models\MixedToOneIdentity;
+
+/** @Entity */
+class CompositeToOneKeyState
+{
+    const CLASSNAME = __CLASS__;
+
+    /**
+     * @Id
+     * @Column(type="string")
+     * @GeneratedValue(strategy="NONE")
+     */
+    public $state;
+
+    /**
+     * @Id
+     * @ManyToOne(targetEntity="Country", cascade={"MERGE"})
+     * @JoinColumn(referencedColumnName="country")
+     */
+    public $country;
+}
\ No newline at end of file
diff --git a/tests/Doctrine/Tests/Models/MixedToOneIdentity/Country.php b/tests/Doctrine/Tests/Models/MixedToOneIdentity/Country.php
new file mode 100644
index 000000000..bbdc237f7
--- /dev/null
+++ b/tests/Doctrine/Tests/Models/MixedToOneIdentity/Country.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace Doctrine\Tests\Models\MixedToOneIdentity;
+
+/** @Entity */
+class Country
+{
+    const CLASSNAME = __CLASS__;
+
+    /** @Id @Column(type="string") @GeneratedValue(strategy="NONE") */
+    public $country;
+}
diff --git a/tests/Doctrine/Tests/ORM/Functional/MergeCompositeToOneKeyTest.php b/tests/Doctrine/Tests/ORM/Functional/MergeCompositeToOneKeyTest.php
new file mode 100644
index 000000000..6c6198520
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/MergeCompositeToOneKeyTest.php
@@ -0,0 +1,44 @@
+<?php
+
+namespace Doctrine\Tests\ORM\Functional;
+
+use Doctrine\Tests\Models\MixedToOneIdentity\CompositeToOneKeyState;
+use Doctrine\Tests\Models\MixedToOneIdentity\Country;
+
+class MergeCompositeToOneKeyTest extends \Doctrine\Tests\OrmFunctionalTestCase
+{
+    /**
+     * {@inheritDoc}
+     */
+    protected function setUp()
+    {
+        parent::setUp();
+
+        $this->_schemaTool->createSchema(array(
+            $this->_em->getClassMetadata(Country::CLASSNAME),
+            $this->_em->getClassMetadata(CompositeToOneKeyState::CLASSNAME),
+        ));
+    }
+
+    /**
+     * @group DDC-3378
+     * @group 1176
+     */
+    public function testMergingOfEntityWithCompositeIdentifierContainingToOneAssociation()
+    {
+        $country = new Country();
+        $country->country = 'US';
+
+        $state = new CompositeToOneKeyState();
+        $state->state   = 'CA';
+        $state->country = $country;
+
+        /* @var $merged CompositeToOneKeyState */
+        $merged = $this->_em->merge($state);
+
+        $this->assertInstanceOf(CompositeToOneKeyState::CLASSNAME, $state);
+        $this->assertNotSame($state, $merged);
+        $this->assertInstanceOf(Country::CLASSNAME, $merged->country);
+        $this->assertNotSame($country, $merged->country);
+    }
+}