diff --git a/docs/en/cookbook/custom-mapping-types.rst b/docs/en/cookbook/custom-mapping-types.rst
index 27ada30ee..1bd4f1242 100644
--- a/docs/en/cookbook/custom-mapping-types.rst
+++ b/docs/en/cookbook/custom-mapping-types.rst
@@ -13,44 +13,50 @@ you wish. Here is an example skeleton of such a custom type class:
 
     <?php
     namespace My\Project\Types;
-    
+
     use Doctrine\DBAL\Types\Type;
     use Doctrine\DBAL\Platforms\AbstractPlatform;
-    
+
     /**
      * My custom datatype.
      */
     class MyType extends Type
     {
         const MYTYPE = 'mytype'; // modify to match your type name
-    
+
         public function getSQLDeclaration(array $fieldDeclaration, AbstractPlatform $platform)
         {
             // return the SQL used to create your column type. To create a portable column type, use the $platform.
         }
-    
+
         public function convertToPHPValue($value, AbstractPlatform $platform)
         {
             // This is executed when the value is read from the database. Make your conversions here, optionally using the $platform.
         }
-    
+
         public function convertToDatabaseValue($value, AbstractPlatform $platform)
         {
             // This is executed when the value is written to the database. Make your conversions here, optionally using the $platform.
         }
-    
+
         public function getName()
         {
             return self::MYTYPE; // modify to match your constant name
         }
     }
 
-The following assumptions are applied to mapping types by the ORM:
+.. note::
 
--  If the value of the field is *NULL* the method
-   ``convertToDatabaseValue()`` is not called.
--  The ``UnitOfWork`` never passes values to the database convert
-   method that did not change in the request.
+    The following assumptions are applied to mapping types by the ORM:
+
+    -  If the value of the field is *NULL* the method
+       ``convertToDatabaseValue()`` is not called.
+    -  The ``UnitOfWork`` never passes values to the database convert
+       method that did not change in the request.
+    -  The ``UnitOfWork`` internally assumes that entity identifiers are
+       castable to string. Hence, when using custom types that map to PHP
+       objects as IDs, such objects must implement the ``__toString()`` magic
+       method.
 
 When you have implemented the type you still need to let Doctrine
 know about it. This can be achieved through the
diff --git a/lib/Doctrine/ORM/UnitOfWork.php b/lib/Doctrine/ORM/UnitOfWork.php
index 0126bc628..80915155d 100644
--- a/lib/Doctrine/ORM/UnitOfWork.php
+++ b/lib/Doctrine/ORM/UnitOfWork.php
@@ -1566,15 +1566,17 @@ class UnitOfWork implements PropertyChangedListener
      *
      * @ignore
      *
-     * @param string $idHash
+     * @param mixed  $idHash        (must be possible to cast it to string)
      * @param string $rootClassName
      *
      * @return object|bool The found entity or FALSE.
      */
     public function tryGetByIdHash($idHash, $rootClassName)
     {
-        if (isset($this->identityMap[$rootClassName][$idHash])) {
-            return $this->identityMap[$rootClassName][$idHash];
+        $stringIdHash = (string) $idHash;
+
+        if (isset($this->identityMap[$rootClassName][$stringIdHash])) {
+            return $this->identityMap[$rootClassName][$stringIdHash];
         }
 
         return false;
diff --git a/tests/Doctrine/Tests/DbalTypes/CustomIdObject.php b/tests/Doctrine/Tests/DbalTypes/CustomIdObject.php
new file mode 100644
index 000000000..df34ebccb
--- /dev/null
+++ b/tests/Doctrine/Tests/DbalTypes/CustomIdObject.php
@@ -0,0 +1,44 @@
+<?php
+/*
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * This software consists of voluntary contributions made by many individuals
+ * and is licensed under the MIT license. For more information, see
+ * <http://www.doctrine-project.org>.
+ */
+
+namespace Doctrine\Tests\DbalTypes;
+
+class CustomIdObject
+{
+    /**
+     * @var string
+     */
+    public $id;
+
+    /**
+     * @param string $id
+     */
+    public function __construct($id)
+    {
+        $this->id = (string) $id;
+    }
+
+    /**
+     * @return string
+     */
+    public function __toString()
+    {
+        return $this->id;
+    }
+}
diff --git a/tests/Doctrine/Tests/DbalTypes/CustomIdObjectType.php b/tests/Doctrine/Tests/DbalTypes/CustomIdObjectType.php
new file mode 100644
index 000000000..3d5aa0c19
--- /dev/null
+++ b/tests/Doctrine/Tests/DbalTypes/CustomIdObjectType.php
@@ -0,0 +1,63 @@
+<?php
+/*
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * This software consists of voluntary contributions made by many individuals
+ * and is licensed under the MIT license. For more information, see
+ * <http://www.doctrine-project.org>.
+ */
+
+namespace Doctrine\Tests\DbalTypes;
+
+use Doctrine\DBAL\Platforms\AbstractPlatform;
+use Doctrine\DBAL\Types\Type;
+
+class CustomIdObjectType extends Type
+{
+    const NAME      = 'CustomIdObject';
+    const CLASSNAME = __CLASS__;
+
+    /**
+     * {@inheritdoc}
+     */
+    public function convertToDatabaseValue($value, AbstractPlatform $platform)
+    {
+        return $value->id;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function convertToPHPValue($value, AbstractPlatform $platform)
+    {
+        $idObject = new CustomIdObject($value);
+
+        return $idObject;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getSQLDeclaration(array $fieldDeclaration, AbstractPlatform $platform)
+    {
+        return $platform->getVarcharTypeDeclarationSQL($fieldDeclaration);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getName()
+    {
+        return self::NAME;
+    }
+}
diff --git a/tests/Doctrine/Tests/Models/CustomType/CustomIdObjectTypeChild.php b/tests/Doctrine/Tests/Models/CustomType/CustomIdObjectTypeChild.php
new file mode 100644
index 000000000..028a55c25
--- /dev/null
+++ b/tests/Doctrine/Tests/Models/CustomType/CustomIdObjectTypeChild.php
@@ -0,0 +1,53 @@
+<?php
+/*
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * This software consists of voluntary contributions made by many individuals
+ * and is licensed under the MIT license. For more information, see
+ * <http://www.doctrine-project.org>.
+ */
+
+namespace Doctrine\Tests\Models\CustomType;
+
+use Doctrine\Tests\DbalTypes\CustomIdObject;
+
+/**
+ * @Entity
+ * @Table(name="custom_id_type_child")
+ */
+class CustomIdObjectTypeChild
+{
+    const CLASSNAME = __CLASS__;
+
+    /**
+     * @Id @Column(type="CustomIdObject")
+     *
+     * @var CustomIdObject
+     */
+    public $id;
+
+    /**
+     * @ManyToOne(targetEntity="Doctrine\Tests\Models\CustomType\CustomIdObjectTypeParent", inversedBy="children")
+     */
+    public $parent;
+
+    /**
+     * @param CustomIdObject           $id
+     * @param CustomIdObjectTypeParent $parent
+     */
+    public function __construct(CustomIdObject $id, CustomIdObjectTypeParent $parent)
+    {
+        $this->id     = $id;
+        $this->parent = $parent;
+    }
+}
diff --git a/tests/Doctrine/Tests/Models/CustomType/CustomIdObjectTypeParent.php b/tests/Doctrine/Tests/Models/CustomType/CustomIdObjectTypeParent.php
new file mode 100644
index 000000000..3045c647b
--- /dev/null
+++ b/tests/Doctrine/Tests/Models/CustomType/CustomIdObjectTypeParent.php
@@ -0,0 +1,53 @@
+<?php
+/*
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * This software consists of voluntary contributions made by many individuals
+ * and is licensed under the MIT license. For more information, see
+ * <http://www.doctrine-project.org>.
+ */
+
+namespace Doctrine\Tests\Models\CustomType;
+
+use Doctrine\Tests\DbalTypes\CustomIdObject;
+use Doctrine\Common\Collections\ArrayCollection;
+
+/**
+ * @Entity
+ * @Table(name="custom_id_type_parent")
+ */
+class CustomIdObjectTypeParent
+{
+    const CLASSNAME = __CLASS__;
+
+    /**
+     * @Id @Column(type="CustomIdObject")
+     *
+     * @var CustomIdObject
+     */
+    public $id;
+
+    /**
+     * @OneToMany(targetEntity="Doctrine\Tests\Models\CustomType\CustomIdObjectTypeChild", cascade={"persist", "remove"}, mappedBy="parent")
+     */
+    public $children;
+
+    /**
+     * @param CustomIdObject $id
+     */
+    public function __construct(CustomIdObject $id)
+    {
+        $this->id       = $id;
+        $this->children = new ArrayCollection();
+    }
+}
diff --git a/tests/Doctrine/Tests/ORM/Functional/CustomIdObjectTypeTest.php b/tests/Doctrine/Tests/ORM/Functional/CustomIdObjectTypeTest.php
new file mode 100644
index 000000000..2e7abf76c
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/CustomIdObjectTypeTest.php
@@ -0,0 +1,110 @@
+<?php
+/*
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * This software consists of voluntary contributions made by many individuals
+ * and is licensed under the MIT license. For more information, see
+ * <http://www.doctrine-project.org>.
+ */
+
+namespace Doctrine\Tests\ORM\Functional;
+
+use Doctrine\Tests\DbalTypes\CustomIdObject;
+use Doctrine\Tests\DbalTypes\CustomIdObjectType;
+use Doctrine\Tests\Models\CustomType\CustomIdObjectTypeChild;
+use Doctrine\Tests\Models\CustomType\CustomIdObjectTypeParent;
+use Doctrine\Tests\OrmFunctionalTestCase;
+use Doctrine\DBAL\Types\Type as DBALType;
+
+class CustomIdObjectTypeTest extends OrmFunctionalTestCase
+{
+    protected function setUp()
+    {
+        if (DBALType::hasType(CustomIdObjectType::NAME)) {
+            DBALType::overrideType(CustomIdObjectType::NAME, CustomIdObjectType::CLASSNAME);
+        } else {
+            DBALType::addType(CustomIdObjectType::NAME, CustomIdObjectType::CLASSNAME);
+        }
+
+        $this->useModelSet('custom_id_object_type');
+
+        parent::setUp();
+    }
+
+    public function testFindByCustomIdObject()
+    {
+        $parent = new CustomIdObjectTypeParent(new CustomIdObject('foo'));
+
+        $this->_em->persist($parent);
+        $this->_em->flush();
+
+        $result = $this->_em->find(CustomIdObjectTypeParent::CLASSNAME, $parent->id);
+
+        $this->assertSame($parent, $result);
+    }
+
+    /**
+     * @group DDC-3622
+     * @group 1336
+     */
+    public function testFetchJoinCustomIdObject()
+    {
+        $parent = new CustomIdObjectTypeParent(new CustomIdObject('foo'));
+
+        $parent->children->add(new CustomIdObjectTypeChild(new CustomIdObject('bar'), $parent));
+
+        $this->_em->persist($parent);
+        $this->_em->flush();
+
+        $result = $this
+            ->_em
+            ->createQuery(
+                'SELECT parent, children FROM '
+                . CustomIdObjectTypeParent::CLASSNAME
+                . ' parent LEFT JOIN parent.children children'
+            )
+            ->getResult();
+
+        $this->assertCount(1, $result);
+        $this->assertSame($parent, $result[0]);
+    }
+
+    /**
+     * @group DDC-3622
+     * @group 1336
+     */
+    public function testFetchJoinWhereCustomIdObject()
+    {
+        $parent = new CustomIdObjectTypeParent(new CustomIdObject('foo'));
+
+        $parent->children->add(new CustomIdObjectTypeChild(new CustomIdObject('bar'), $parent));
+
+        $this->_em->persist($parent);
+        $this->_em->flush();
+
+        // note: hydration is willingly broken in this example:
+        $result = $this
+            ->_em
+            ->createQuery(
+                'SELECT parent, children FROM '
+                . CustomIdObjectTypeParent::CLASSNAME
+                . ' parent LEFT JOIN parent.children children '
+                . 'WHERE children.id = ?1'
+            )
+            ->setParameter(1, $parent->children->first()->id)
+            ->getResult();
+
+        $this->assertCount(1, $result);
+        $this->assertSame($parent, $result[0]);
+    }
+}
diff --git a/tests/Doctrine/Tests/OrmFunctionalTestCase.php b/tests/Doctrine/Tests/OrmFunctionalTestCase.php
index 7aaeae81a..ae9f4b43b 100644
--- a/tests/Doctrine/Tests/OrmFunctionalTestCase.php
+++ b/tests/Doctrine/Tests/OrmFunctionalTestCase.php
@@ -257,7 +257,11 @@ abstract class OrmFunctionalTestCase extends OrmTestCase
             'Doctrine\Tests\Models\GeoNames\Admin1',
             'Doctrine\Tests\Models\GeoNames\Admin1AlternateName',
             'Doctrine\Tests\Models\GeoNames\City'
-        )
+        ),
+        'custom_id_object_type' => array(
+            'Doctrine\Tests\Models\CustomType\CustomIdObjectTypeParent',
+            'Doctrine\Tests\Models\CustomType\CustomIdObjectTypeChild',
+        ),
     );
 
     /**
@@ -496,6 +500,11 @@ abstract class OrmFunctionalTestCase extends OrmTestCase
             $conn->executeUpdate('DELETE FROM geonames_country');
         }
 
+        if (isset($this->_usedModelSets['custom_id_object_type'])) {
+            $conn->executeUpdate('DELETE FROM custom_id_type_child');
+            $conn->executeUpdate('DELETE FROM custom_id_type_parent');
+        }
+
         $this->_em->clear();
     }