diff --git a/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php b/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php
index d36ea308464..7a7c2bc6d1a 100644
--- a/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php
+++ b/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php
@@ -31,6 +31,7 @@
 use Doctrine\Persistence\Mapping\ClassMetadata as ClassMetadataInterface;
 use Doctrine\Persistence\Mapping\Driver\MappingDriver;
 use Doctrine\Persistence\Mapping\ReflectionService;
+use ReflectionClass;
 use ReflectionException;
 use function assert;
 use function interface_exists;
@@ -278,6 +279,11 @@ protected function validateRuntimeMetadata($class, $parent)
                 if ( ! $class->discriminatorColumn) {
                     throw MappingException::missingDiscriminatorColumn($class->name);
                 }
+                foreach ($class->subClasses as $subClass) {
+                    if ((new ReflectionClass($subClass))->name !== $subClass) {
+                        throw MappingException::invalidClassInDiscriminatorMap($subClass, $class->name);
+                    }
+                }
             }
         } else if ($class->isMappedSuperclass && $class->name == $class->rootEntityName && (count($class->discriminatorMap) || $class->discriminatorColumn)) {
             // second condition is necessary for mapped superclasses in the middle of an inheritance hierarchy
diff --git a/tests/Doctrine/Tests/ORM/Mapping/AbstractMappingDriverTest.php b/tests/Doctrine/Tests/ORM/Mapping/AbstractMappingDriverTest.php
index 3104cf58d0e..eb2388b9e52 100644
--- a/tests/Doctrine/Tests/ORM/Mapping/AbstractMappingDriverTest.php
+++ b/tests/Doctrine/Tests/ORM/Mapping/AbstractMappingDriverTest.php
@@ -38,6 +38,7 @@
 use Doctrine\Tests\Models\DDC964\DDC964Admin;
 use Doctrine\Tests\Models\DDC964\DDC964Guest;
 use Doctrine\Tests\OrmTestCase;
+use function class_exists;
 
 abstract class AbstractMappingDriverTest extends OrmTestCase
 {
@@ -1087,7 +1088,7 @@ class_exists(CaseSensitiveDiscriminatorMap\Cube::class);
         $this->expectException(MappingException::class);
         $this->expectExceptionMessage('Entity class \'Doctrine\Tests\Models\CaseSensitiveDiscriminatorMap\cube\' used in the discriminator map of class \'Doctrine\Tests\Models\CaseSensitiveDiscriminatorMap\Shape\' does not exist.');
 
-        $em = $this->_getTestEntityManager();
+        $em      = $this->_getTestEntityManager();
         $factory = $this->createClassMetadataFactory($em);
         $factory->getMetadataFor(CaseSensitiveDiscriminatorMap\Shape::class);
     }