diff --git a/lib/Fhp/Syntax/Serializer.php b/lib/Fhp/Syntax/Serializer.php
index 6c2ff267..155263c9 100644
--- a/lib/Fhp/Syntax/Serializer.php
+++ b/lib/Fhp/Syntax/Serializer.php
@@ -130,6 +130,7 @@ private static function serializeElements($obj, BaseDescriptor $descriptor): arr
                         $value === null || $repetition >= count($value) ? null : $value[$repetition],
                         $elementDescriptor->type, $isSegment);
                 }
+                $index += $numOutputElements - 1; // The outer loop will increment by 1 as well.
             }
         }
         return $serializedElements;
diff --git a/lib/Tests/Fhp/Segment/UpdSerializationTest.php b/lib/Tests/Fhp/Segment/UpdSerializationTest.php
new file mode 100644
index 00000000..8df47a6a
--- /dev/null
+++ b/lib/Tests/Fhp/Segment/UpdSerializationTest.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace Fhp\Segment;
+
+use Fhp\Segment\HIUPD\HIUPDv6;
+use Fhp\Syntax\Parser;
+use Fhp\Syntax\Serializer;
+use PHPUnit\Framework\TestCase;
+
+class UpdSerializationTest extends TestCase
+{
+    private const HIUPD = "HIUPD:7:6:4+PRIVAT::280:11223344+DE00112233440000000000+PRIVATE_______+1+EUR+PRIVATE__________________++Kontokorrent++HKSAK:1+HKISA:1+HKSSP:1+HKCAZ:1+HKEKA:1+HKKAU:1+HKCDB:1+HKPSP:1+HKCSL:1+HKCDL:1+HKPAE:1+HKDVK:1+HKPPD:1+HKCSA:1+HKCDN:1+HKBMB:1+HKBBS:1+HKDMB:1+HKDBS:1+HKCSB:1+HKCUB:1+HKKAA:1+HKPOF:1+HKQTG:1+HKSPA:1+HKDSB:1+HKIPZ:1+HKIPS:1+HKCUM:1+HKCCS:1+HKCDE:1+HKCSE:1+HKDSW:1+HKSAL:1+HKKIF:1+HKKAZ:1+HKAUB:1+GKVPU:1+GKVPD:1+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++{\"umsltzt\"?:\"2025-10-10-10.32.13.000636\"}'";
+
+    public function testParserPlusSerializer(): void
+    {
+        /** @var HIUPDv6 $hiupd */
+        $hiupd = Parser::parseSegment(static::HIUPD, HIUPDv6::class);
+        $this->assertEquals(static::HIUPD, Serializer::serializeSegment($hiupd));
+    }
+
+    public function testNativePhpSerialization(): void
+    {
+        /** @var HIUPDv6 $hiupd */
+        $hiupd = Parser::parseSegment(static::HIUPD, HIUPDv6::class);
+        $before = $hiupd->getErlaubteGeschaeftsvorfaelle();
+
+        /** @var HIUPDv6 $hiupd */
+        $hiupd = unserialize(serialize($hiupd));
+        $after = $hiupd->getErlaubteGeschaeftsvorfaelle();
+
+        $this->assertEquals($before, $after);
+    }
+}