diff --git a/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php b/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
index 62bca42d9c7..cbd37b3433e 100644
--- a/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
+++ b/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
@@ -3225,6 +3225,14 @@ final public function getDiscriminatorColumn(): array
      */
     public function setDiscriminatorMap(array $map)
     {
+        if (count(array_flip($map)) !== count($map)) {
+            Deprecation::trigger(
+                'doctrine/orm',
+                'https://github.com/doctrine/orm/issues/3519',
+                'Mapping a class to multiple discriminator values is deprecated.'
+            );
+        }
+
         foreach ($map as $value => $className) {
             $this->addDiscriminatorMapClass($value, $className);
         }
diff --git a/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php b/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php
index 6776da4f85f..9c673ef4c77 100644
--- a/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php
+++ b/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php
@@ -5,6 +5,7 @@
 namespace Doctrine\Tests\ORM\Mapping;
 
 use ArrayObject;
+use Doctrine\Deprecations\PHPUnit\VerifyDeprecations;
 use Doctrine\ORM\Events;
 use Doctrine\ORM\Mapping\ClassMetadata;
 use Doctrine\ORM\Mapping\Column;
@@ -45,6 +46,8 @@
 
 class ClassMetadataTest extends OrmTestCase
 {
+    use VerifyDeprecations;
+
     public function testClassMetadataInstanceSerialization(): void
     {
         $cm = new ClassMetadata(CMS\CmsUser::class);
@@ -1366,6 +1369,14 @@ public function testInlineEmbeddable(): void
 
         self::assertTrue($classMetadata->hasField('test'));
     }
+
+    public function testDiscriminatorMapWithSameClassMultipleTimesDeprecated(): void
+    {
+        $this->expectDeprecationWithIdentifier('https://github.com/doctrine/orm/issues/3519');
+
+        $cm = new ClassMetadata(CMS\CmsUser::class);
+        $cm->setDiscriminatorMap(['foo' => CMS\CmsUser::class, 'bar' => CMS\CmsUser::class]);
+    }
 }
 
 /**