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/Models/CaseSensitiveDiscriminatorMap/Cube.php b/tests/Doctrine/Tests/Models/CaseSensitiveDiscriminatorMap/Cube.php
new file mode 100644
index 00000000000..0c608f7453b
--- /dev/null
+++ b/tests/Doctrine/Tests/Models/CaseSensitiveDiscriminatorMap/Cube.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\Models\CaseSensitiveDiscriminatorMap;
+
+/** @Entity */
+final class Cube extends Shape
+{
+}
diff --git a/tests/Doctrine/Tests/Models/CaseSensitiveDiscriminatorMap/Shape.php b/tests/Doctrine/Tests/Models/CaseSensitiveDiscriminatorMap/Shape.php
new file mode 100644
index 00000000000..f7ca03c281f
--- /dev/null
+++ b/tests/Doctrine/Tests/Models/CaseSensitiveDiscriminatorMap/Shape.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\Models\CaseSensitiveDiscriminatorMap;
+
+use Doctrine\ORM\Mapping\ClassMetadataInfo;
+
+/**
+ * @Entity
+ * @InheritanceType("SINGLE_TABLE")
+ * @DiscriminatorMap({"cube" = cube::class})
+ * @DiscriminatorColumn(name="discr", length=32, type="string")
+ */
+abstract class Shape
+{
+    /** @Id @Column(type="string") @GeneratedValue(strategy="AUTO") */
+    public $id;
+
+    public static function loadMetadata(ClassMetadataInfo $metadata)
+    {
+        $metadata->setInheritanceType(ClassMetadataInfo::INHERITANCE_TYPE_SINGLE_TABLE);
+        $metadata->setDiscriminatorColumn([
+            'name' => 'discr',
+            'type' => 'string',
+            'length' => 32,
+        ]);
+        $metadata->setDiscriminatorMap([
+            'cube' => cube::class,
+        ]);
+        $metadata->mapField([
+            'fieldName' => 'id',
+            'type' => 'string',
+            'length' => null,
+            'precision' => 0,
+            'scale' => 0,
+            'nullable' => false,
+            'unique' => false,
+            'id' => true,
+            'columnName' => 'id',
+        ]);
+        $metadata->setIdGeneratorType(ClassMetadataInfo::GENERATOR_TYPE_AUTO);
+    }
+}
diff --git a/tests/Doctrine/Tests/ORM/Mapping/AbstractMappingDriverTest.php b/tests/Doctrine/Tests/ORM/Mapping/AbstractMappingDriverTest.php
index 502ed479e28..eb2388b9e52 100644
--- a/tests/Doctrine/Tests/ORM/Mapping/AbstractMappingDriverTest.php
+++ b/tests/Doctrine/Tests/ORM/Mapping/AbstractMappingDriverTest.php
@@ -14,6 +14,7 @@
 use Doctrine\ORM\Mapping\UnderscoreNamingStrategy;
 use Doctrine\Persistence\Mapping\RuntimeReflectionService;
 use Doctrine\Tests\Models\Cache\City;
+use Doctrine\Tests\Models\CaseSensitiveDiscriminatorMap;
 use Doctrine\Tests\Models\CMS\CmsAddress;
 use Doctrine\Tests\Models\CMS\CmsAddressListener;
 use Doctrine\Tests\Models\CMS\CmsUser;
@@ -37,6 +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
 {
@@ -1079,6 +1081,17 @@ public function testDiscriminatorColumnDefaultName()
         $this->assertEquals('dtype', $class->discriminatorColumn['name']);
     }
 
+    public function testInvalidSubClassCase()
+    {
+        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();
+        $factory = $this->createClassMetadataFactory($em);
+        $factory->getMetadataFor(CaseSensitiveDiscriminatorMap\Shape::class);
+    }
 }
 
 /**
@@ -1344,7 +1357,6 @@ public static function loadMetadata(ClassMetadataInfo $metadata)
     }
 }
 
-
 /**
  * @Entity
  */
diff --git a/tests/Doctrine/Tests/ORM/Mapping/php/Doctrine.Tests.Models.CaseSensitiveDiscriminatorMap.Shape.php b/tests/Doctrine/Tests/ORM/Mapping/php/Doctrine.Tests.Models.CaseSensitiveDiscriminatorMap.Shape.php
new file mode 100644
index 00000000000..5299f8246c9
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Mapping/php/Doctrine.Tests.Models.CaseSensitiveDiscriminatorMap.Shape.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+use Doctrine\ORM\Mapping\ClassMetadataInfo;
+use Doctrine\Tests\Models\CaseSensitiveDiscriminatorMap\cube;
+
+$metadata->setInheritanceType(ClassMetadataInfo::INHERITANCE_TYPE_SINGLE_TABLE);
+$metadata->setDiscriminatorColumn([
+    'name' => 'discr',
+    'type' => 'string',
+    'length' => 32,
+]);
+$metadata->setDiscriminatorMap([
+    'cube' => cube::class,
+]);
+$metadata->mapField([
+    'fieldName' => 'id',
+    'type' => 'string',
+    'length' => null,
+    'precision' => 0,
+    'scale' => 0,
+    'nullable' => false,
+    'unique' => false,
+    'id' => true,
+    'columnName' => 'id',
+]);
+$metadata->setIdGeneratorType(ClassMetadataInfo::GENERATOR_TYPE_AUTO);
diff --git a/tests/Doctrine/Tests/ORM/Mapping/xml/Doctrine.Tests.Models.CaseSensitiveDiscriminatorMap.Shape.dcm.xml b/tests/Doctrine/Tests/ORM/Mapping/xml/Doctrine.Tests.Models.CaseSensitiveDiscriminatorMap.Shape.dcm.xml
new file mode 100644
index 00000000000..51139c14bc3
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Mapping/xml/Doctrine.Tests.Models.CaseSensitiveDiscriminatorMap.Shape.dcm.xml
@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<doctrine-mapping xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
+      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+      xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping
+                          https://www.doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
+    <entity name="Doctrine\Tests\Models\CaseSensitiveDiscriminatorMap\Shape" inheritance-type="SINGLE_TABLE">
+        <discriminator-column name="discr" type="string" length="32" />
+        <discriminator-map>
+            <discriminator-mapping value="cube" class="Doctrine\Tests\Models\CaseSensitiveDiscriminatorMap\cube" />
+        </discriminator-map>
+        <id name="id" type="integer" column="id">
+            <generator strategy="AUTO" />
+        </id>
+    </entity>
+</doctrine-mapping>
diff --git a/tests/Doctrine/Tests/ORM/Mapping/yaml/Doctrine.Tests.Models.CaseSensitiveDiscriminatorMap.Shape.dcm.yml b/tests/Doctrine/Tests/ORM/Mapping/yaml/Doctrine.Tests.Models.CaseSensitiveDiscriminatorMap.Shape.dcm.yml
new file mode 100644
index 00000000000..062f9ddc99f
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Mapping/yaml/Doctrine.Tests.Models.CaseSensitiveDiscriminatorMap.Shape.dcm.yml
@@ -0,0 +1,14 @@
+Doctrine\Tests\Models\CaseSensitiveDiscriminatorMap\Shape:
+  type: entity
+  inheritanceType: SINGLE_TABLE
+  discriminatorMap:
+    cube: Doctrine\Tests\Models\CaseSensitiveDiscriminatorMap\cube
+  discriminatorColumn:
+    type: string
+    name: discr
+    length: 32
+  id:
+    id:
+      type: integer
+      generator:
+        strategy: AUTO