diff --git a/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php b/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php
index bf802ecf9..b327c5073 100644
--- a/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php
+++ b/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php
@@ -164,13 +164,11 @@ class ClassMetadataFactory implements ClassMetadataFactoryInterface
             }
 
             if ($this->cacheDriver) {
-                if (($cached = $this->cacheDriver->fetch("$realClassName\$CLASSMETADATA")) !== false) {
+                if (($cached = $this->fetchMetadataFromCache($realClassName)) !== false) {
                     $this->loadedMetadata[$realClassName] = $cached;
                 } else {
                     foreach ($this->loadMetadata($realClassName) as $loadedClassName) {
-                        $this->cacheDriver->save(
-                            "$loadedClassName\$CLASSMETADATA", $this->loadedMetadata[$loadedClassName], null
-                        );
+                        $this->cacheMetadata($loadedClassName, $this->loadedMetadata[$loadedClassName]);
                     }
                 }
             } else {
@@ -319,6 +317,11 @@ class ClassMetadataFactory implements ClassMetadataFactoryInterface
 
             $class->setParentClasses($visited);
 
+            // Calculate Discriminator Map if needed and if no discriminator map is set
+            if ($class->isInheritanceTypeJoined() && empty($class->discriminatorMap)) {
+                $this->addDefaultDiscriminatorMap($class);
+            }
+
             if ($this->evm->hasListeners(Events::loadClassMetadata)) {
                 $eventArgs = new \Doctrine\ORM\Event\LoadClassMetadataEventArgs($class, $this->em);
                 $this->evm->dispatchEvent(Events::loadClassMetadata, $eventArgs);
@@ -388,6 +391,89 @@ class ClassMetadataFactory implements ClassMetadataFactoryInterface
         return new ClassMetadata($className);
     }
 
+    /**
+     * Adds a default discriminator map if no one is given
+     *
+     * @param \Doctrine\ORM\Mapping\ClassMetadata $class
+     */
+    private function addDefaultDiscriminatorMap(ClassMetadata $class)
+    {
+        $allClasses = $this->driver->getAllClassNames();
+        $subClassesMetadata = array();
+        $fqcn = $class->getName();
+        $map = array(str_replace('\\', '.', $fqcn) => $fqcn);
+
+        foreach ($allClasses as $c) {
+            if (is_subclass_of($c, $fqcn)) {
+                if (isset($this->loadedMetadata[$c])) {
+                    $subClassMetadata = $this->loadedMetadata[$c];
+                } else {
+                    $subClassMetadata = $this->newClassMetadataInstance($c);
+                    $this->driver->loadMetadataForClass($c, $subClassMetadata);
+                }
+
+                if (!$subClassMetadata->isMappedSuperclass) {
+                    $map[str_replace('\\', '.', $c)] = $c;
+                    $subClassesMetadata[$c] = $subClassMetadata;
+                }
+            }
+        }
+
+        $class->setDiscriminatorMap($map);
+
+        // Now we set the discriminator map for the subclasses already loaded
+        foreach ($subClassesMetadata as $subClassFqcn => $subClassMetadata) {
+            $subClassMetadata->setDiscriminatorMap($map);
+
+            // We need to overwrite the cached version of the metadata, because
+            // it was cached without the discriminator map
+            if ($this->cacheDriver && $this->cacheContainsMetadata($subClassFqcn)) {
+                // If subclass metadata is not already loaded, it's incomplete so
+                // we reload it again from cache
+                if (!isset($this->loadedMetadata[$subClassFqcn])) {
+                    $subClassMetadata = $this->fetchMetadataFromCache($subClassFqcn);
+                    $subClassMetadata->setDiscriminatorMap($map);
+                }
+
+                $this->cacheMetadata($subClassFqcn, $subClassMetadata);
+            }
+        }
+    }
+
+    /**
+     * Cache the metadata
+     *
+     * @param $className
+     * @param \Doctrine\ORM\Mapping\ClassMetadata $metadata
+     */
+    private function cacheMetadata($className, ClassMetadata $metadata)
+    {
+        $this->cacheDriver->save(
+            "$className\$CLASSMETADATA", $metadata, null
+        );
+    }
+
+    /**
+     * Verify if metadata is cached
+     *
+     * @param $className
+     * @return bool
+     */
+    private function cacheContainsMetadata($className)
+    {
+        return $this->cacheDriver->contains("$className\$CLASSMETADATA");
+    }
+
+    /**
+     * Fetch metadata from cache
+     *
+     * @param $className
+     */
+    private function fetchMetadataFromCache($className)
+    {
+        return $this->cacheDriver->fetch("$className\$CLASSMETADATA");
+    }
+
     /**
      * Adds inherited fields to the subclass mapping.
      *
diff --git a/tests/Doctrine/Tests/Models/JoinedInheritanceType/AnotherChildClass.php b/tests/Doctrine/Tests/Models/JoinedInheritanceType/AnotherChildClass.php
new file mode 100644
index 000000000..e49d89807
--- /dev/null
+++ b/tests/Doctrine/Tests/Models/JoinedInheritanceType/AnotherChildClass.php
@@ -0,0 +1,10 @@
+<?php
+
+namespace Doctrine\Tests\Models\JoinedInheritanceType;
+
+/**
+ * @Entity
+ */
+class AnotherChildClass extends ChildClass
+{
+}
\ No newline at end of file
diff --git a/tests/Doctrine/Tests/Models/JoinedInheritanceType/ChildClass.php b/tests/Doctrine/Tests/Models/JoinedInheritanceType/ChildClass.php
new file mode 100644
index 000000000..35887c768
--- /dev/null
+++ b/tests/Doctrine/Tests/Models/JoinedInheritanceType/ChildClass.php
@@ -0,0 +1,10 @@
+<?php
+
+namespace Doctrine\Tests\Models\JoinedInheritanceType;
+
+/**
+ * @MappedSuperclass
+ */
+abstract class ChildClass extends RootClass
+{
+}
\ No newline at end of file
diff --git a/tests/Doctrine/Tests/Models/JoinedInheritanceType/RootClass.php b/tests/Doctrine/Tests/Models/JoinedInheritanceType/RootClass.php
new file mode 100644
index 000000000..e8b643a82
--- /dev/null
+++ b/tests/Doctrine/Tests/Models/JoinedInheritanceType/RootClass.php
@@ -0,0 +1,16 @@
+<?php
+
+namespace Doctrine\Tests\Models\JoinedInheritanceType;
+
+/**
+ * @Entity
+ * @InheritanceType("JOINED")
+ */
+class RootClass
+{
+    /**
+     * @Column(type="integer")
+     * @Id @GeneratedValue
+     */
+    public $id;
+}
\ No newline at end of file
diff --git a/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataFactoryTest.php b/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataFactoryTest.php
index 223ef8582..6b5c80b70 100644
--- a/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataFactoryTest.php
+++ b/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataFactoryTest.php
@@ -127,6 +127,45 @@ class ClassMetadataFactoryTest extends \Doctrine\Tests\OrmTestCase
         $this->assertTrue($em->getMetadataFactory()->isTransient('CMS:CmsUser'));
         $this->assertFalse($em->getMetadataFactory()->isTransient('CMS:CmsArticle'));
     }
+    
+    public function testAddDefaultDiscriminatorMap()
+    {
+        $cmf = new ClassMetadataFactory();
+        $driver = $this->createAnnotationDriver(array(__DIR__ . '/../../Models/JoinedInheritanceType/'));
+        $em = $this->_createEntityManager($driver);
+        $cmf->setEntityManager($em);
+
+        $rootMetadata = $cmf->getMetadataFor('Doctrine\Tests\Models\JoinedInheritanceType\RootClass');
+        $childMetadata = $cmf->getMetadataFor('Doctrine\Tests\Models\JoinedInheritanceType\ChildClass');
+        $anotherChildMetadata = $cmf->getMetadataFor('Doctrine\Tests\Models\JoinedInheritanceType\AnotherChildClass');
+        $rootDiscriminatorMap = $rootMetadata->discriminatorMap;
+        $childDiscriminatorMap = $childMetadata->discriminatorMap;
+        $anotherChildDiscriminatorMap = $anotherChildMetadata->discriminatorMap;
+
+        $rootClass = 'Doctrine\Tests\Models\JoinedInheritanceType\RootClass';
+        $childClass = 'Doctrine\Tests\Models\JoinedInheritanceType\ChildClass';
+        $anotherChildClass = 'Doctrine\Tests\Models\JoinedInheritanceType\AnotherChildClass';
+
+        $rootClassKey = array_search($rootClass, $rootDiscriminatorMap);
+        $childClassKey = array_search($childClass, $rootDiscriminatorMap);
+        $anotherChildClassKey = array_search($anotherChildClass, $rootDiscriminatorMap);
+
+        $this->assertEquals(str_replace('\\', '.', $rootClass), $rootClassKey);
+        $this->assertFalse($childClassKey);
+        $this->assertEquals(str_replace('\\', '.', $anotherChildClassKey), $anotherChildClassKey);
+
+        $this->assertEquals($childDiscriminatorMap, $rootDiscriminatorMap);
+        $this->assertEquals($anotherChildDiscriminatorMap, $rootDiscriminatorMap);
+
+        // ClassMetadataFactory::addDefaultDiscriminatorMap shouldn't be called again, because the
+        // discriminator map is already cached
+        $cmf = $this->getMock('Doctrine\ORM\Mapping\ClassMetadataFactory', array('addDefaultDiscriminatorMap'));
+        $cmf->setEntityManager($em);
+        $cmf->expects($this->never())
+            ->method('addDefaultDiscriminatorMap');
+
+        $rootMetadata = $cmf->getMetadataFor('Doctrine\Tests\Models\JoinedInheritanceType\RootClass');
+    }
 
     protected function _createEntityManager($metadataDriver)
     {