diff --git a/src/XML/ds/SignatureMethod.php b/src/XML/ds/SignatureMethod.php
index 095e1ecb..c067c346 100644
--- a/src/XML/ds/SignatureMethod.php
+++ b/src/XML/ds/SignatureMethod.php
@@ -8,9 +8,16 @@
 use SimpleSAML\Assert\Assert;
 use SimpleSAML\XML\Exception\InvalidDOMElementException;
 use SimpleSAML\XML\Exception\SchemaViolationException;
+use SimpleSAML\XML\Exception\TooManyElementsException;
+use SimpleSAML\XML\ExtendableElementTrait;
+use SimpleSAML\XML\XsNamespace as NS;
 use SimpleSAML\XMLSecurity\Constants as C;
 use SimpleSAML\XMLSecurity\Exception\InvalidArgumentException;
 
+use function array_keys;
+use function array_merge;
+use function array_pop;
+
 /**
  * Class representing a ds:SignatureMethod element.
  *
@@ -18,13 +25,23 @@
  */
 final class SignatureMethod extends AbstractDsElement
 {
+    use ExtendableElementTrait;
+
+    /** The namespace-attribute for the xs:any element */
+    public const XS_ANY_ELT_NAMESPACE = NS::OTHER;
+
+
     /**
      * Initialize a SignatureMethod element.
      *
      * @param string $Algorithm
+     * @param \SimpleSAML\XMLSecurity\ds\HMACOutputLength|null $hmacOutputLength
+     * @param array<\SimpleSAML\XML\SerializableElementInterface> $children
      */
     public function __construct(
         protected string $Algorithm,
+        protected ?HMACOutputLength $hmacOutputLength = null,
+        array $children = [],
     ) {
         Assert::validURI($Algorithm, SchemaViolationException::class);
         Assert::oneOf(
@@ -36,6 +53,8 @@ public function __construct(
             'Invalid signature method: %s',
             InvalidArgumentException::class,
         );
+
+        $this->setElements($children);
     }
 
 
@@ -50,6 +69,17 @@ public function getAlgorithm(): string
     }
 
 
+    /**
+     * Collect the value of the hmacOutputLength-property
+     *
+     * @return \SimpleSAML\XMLSecurity\ds\HMACOutputLength|null
+     */
+    public function getHMACOutputLength(): ?HMACOutputLength
+    {
+        return $this->hmacOutputLength;
+    }
+
+
     /**
      * Convert XML into a SignatureMethod
      *
@@ -66,7 +96,10 @@ public static function fromXML(DOMElement $xml): static
 
         $Algorithm = SignatureMethod::getAttribute($xml, 'Algorithm');
 
-        return new static($Algorithm);
+        $hmacOutputLength = HMACOutputLength::getChildrenOfClass($xml);
+        Assert::maxCount($hmacOutputLength, 1, TooManyElementsException::class);
+
+        return new static($Algorithm, array_pop($hmacOutputLength), self::getChildElementsFromXML($xml));
     }
 
 
@@ -81,6 +114,12 @@ public function toXML(DOMElement $parent = null): DOMElement
         $e = $this->instantiateParentElement($parent);
         $e->setAttribute('Algorithm', $this->getAlgorithm());
 
+        $this->getHMACOutputLength()?->toXML($e);
+
+        foreach ($this->getElements() as $elt) {
+            $elt->toXML($e);
+        }
+
         return $e;
     }
 }
diff --git a/tests/XML/ds/SignatureMethodTest.php b/tests/XML/ds/SignatureMethodTest.php
index 62097e7b..b89e490a 100644
--- a/tests/XML/ds/SignatureMethodTest.php
+++ b/tests/XML/ds/SignatureMethodTest.php
@@ -6,11 +6,13 @@
 
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\TestCase;
+use SimpleSAML\XML\Chunk;
 use SimpleSAML\XML\DOMDocumentFactory;
 use SimpleSAML\XML\TestUtils\SchemaValidationTestTrait;
 use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
 use SimpleSAML\XMLSecurity\Constants as C;
 use SimpleSAML\XMLSecurity\XML\ds\AbstractDsElement;
+use SimpleSAML\XMLSecurity\XML\ds\HMACOutputLength;
 use SimpleSAML\XMLSecurity\XML\ds\SignatureMethod;
 
 use function dirname;
@@ -34,7 +36,7 @@ public static function setUpBeforeClass(): void
     {
         self::$testedClass = SignatureMethod::class;
 
-        self::$schemaFile = dirname(__FILE__, 4) . '/resources/schemas/xmldsig1-schema.xsd';
+        self::$schemaFile = dirname(__FILE__, 3) . '/resources/schemas/simplesamlphp.xsd';
 
         self::$xmlRepresentation = DOMDocumentFactory::fromFile(
             dirname(__FILE__, 3) . '/resources/xml/ds_SignatureMethod.xml',
@@ -46,7 +48,13 @@ public static function setUpBeforeClass(): void
      */
     public function testMarshalling(): void
     {
-        $signatureMethod = new SignatureMethod(C::SIG_RSA_SHA256);
+        $hmacOutputLength = new HMACOutputLength('1234');
+
+        $chunk = new Chunk(DOMDocumentFactory::fromString(
+            '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">Some</ssp:Chunk>',
+        )->documentElement);
+
+        $signatureMethod = new SignatureMethod(C::SIG_RSA_SHA256, $hmacOutputLength, [$chunk]);
 
         $this->assertEquals(
             self::$xmlRepresentation->saveXML(self::$xmlRepresentation->documentElement),
diff --git a/tests/resources/schemas/simplesamlphp.xsd b/tests/resources/schemas/simplesamlphp.xsd
new file mode 100644
index 00000000..7ce40447
--- /dev/null
+++ b/tests/resources/schemas/simplesamlphp.xsd
@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE schema
+  PUBLIC "-//W3C//DTD XMLSchema 200102//EN" "http://www.w3.org/2001/XMLSchema.dtd"
+ [
+   <!ATTLIST schema 
+     xmlns:ds CDATA #FIXED "urn:x-simplesamlphp:namespace">
+   <!ENTITY ssp 'urn:x-simplesamlphp:namespace'>
+   <!ENTITY % p ''>
+   <!ENTITY % s ''>
+  ]>
+
+<!-- Schema for SimpleSAMLphp dummy classes -->
+
+
+<schema xmlns="http://www.w3.org/2001/XMLSchema"
+        xmlns:ssp="urn:x-simplesamlphp:namespace"
+        xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
+        targetNamespace="urn:x-simplesamlphp:namespace"
+        version="0.1" elementFormDefault="qualified"> 
+
+<import namespace='http://www.w3.org/2000/09/xmldsig#'
+          schemaLocation='../../../resources/schemas/xmldsig1-schema.xsd'/>
+
+<!-- Start Chunk -->
+
+<element name="Chunk" type="string"/>
+
+<!-- End Chunk -->
+
+</schema>
+
diff --git a/tests/resources/xml/ds_SignatureMethod.xml b/tests/resources/xml/ds_SignatureMethod.xml
index 2dccda50..0ddb104f 100644
--- a/tests/resources/xml/ds_SignatureMethod.xml
+++ b/tests/resources/xml/ds_SignatureMethod.xml
@@ -1 +1,4 @@
-<ds:SignatureMethod xmlns:ds="http://www.w3.org/2000/09/xmldsig#" Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256" />
+<ds:SignatureMethod xmlns:ds="http://www.w3.org/2000/09/xmldsig#" Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256">
+  <ds:HMACOutputLength>1234</ds:HMACOutputLength>
+  <ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">Some</ssp:Chunk>
+</ds:SignatureMethod>