diff --git a/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php b/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
index 411357af7..1e038d659 100644
--- a/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
+++ b/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
@@ -1487,6 +1487,10 @@ class ClassMetadataInfo implements ClassMetadata
         $mapping['orphanRemoval']   = isset($mapping['orphanRemoval']) ? (bool) $mapping['orphanRemoval'] : false;
         $mapping['isCascadeRemove'] = $mapping['orphanRemoval'] ? true : $mapping['isCascadeRemove'];
 
+        if ($mapping['orphanRemoval']) {
+            unset($mapping['unique']);
+        }
+
         if (isset($mapping['id']) && $mapping['id'] === true && !$mapping['isOwningSide']) {
             throw MappingException::illegalInverseIdentifierAssociation($this->name, $mapping['fieldName']);
         }
diff --git a/tests/Doctrine/Tests/ORM/Functional/Ticket/DDC1666Test.php b/tests/Doctrine/Tests/ORM/Functional/Ticket/DDC1666Test.php
new file mode 100644
index 000000000..e664e537c
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/Ticket/DDC1666Test.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\Tests\Models\CMS\CmsUser;
+use Doctrine\Tests\Models\CMS\CmsEmail;
+
+/**
+ * @group DDC-1666
+ */
+class DDC1666Test extends \Doctrine\Tests\OrmFunctionalTestCase
+{
+    public function setUp()
+    {
+        $this->useModelSet('cms');
+        parent::setUp();
+    }
+
+    public function testGivenOrphanRemovalOneToOne_WhenReplacing_ThenNoUniqueConstraintError()
+    {
+        $user = new CmsUser();
+        $user->name = "Benjamin";
+        $user->username = "beberlei";
+        $user->status = "something";
+        $user->setEmail($email = new CmsEmail());
+        $email->setEmail("kontakt@beberlei.de");
+
+        $this->_em->persist($user);
+        $this->_em->flush();
+
+        $this->assertTrue($this->_em->contains($email));
+
+        $user->setEmail($newEmail = new CmsEmail());
+        $newEmail->setEmail("benjamin.eberlei@googlemail.com");
+
+        $this->_em->flush();
+
+        $this->assertFalse($this->_em->contains($email));
+    }
+}