diff --git a/modules/saml/lib/Message.php b/modules/saml/lib/Message.php
index 4022a90082034947f02ef5d5a6e886ea9718c542..9dd11c65f542c98f5ba05eb68d42982418000124 100644
--- a/modules/saml/lib/Message.php
+++ b/modules/saml/lib/Message.php
@@ -17,7 +17,7 @@ class sspmod_saml_Message {
 	 * @param SimpleSAML_Configuration $dstMetadata  The metadata of the recipient.
 	 * @param SAML2_Message $element  The element we should add the data to.
 	 */
-	public static function addSign(SimpleSAML_Configuration $srcMetadata, SimpleSAML_Configuration $dstMetadata, SAML2_SignedElement $element) {
+	public static function addSign(SimpleSAML_Configuration $srcMetadata, SimpleSAML_Configuration $dstMetadata = NULL, SAML2_SignedElement $element) {
 
 		$keyArray = SimpleSAML_Utilities::loadPrivateKey($srcMetadata, TRUE);
 		$certArray = SimpleSAML_Utilities::loadPublicKey($srcMetadata, FALSE);
diff --git a/www/saml2/idp/ArtifactResolutionService.php b/www/saml2/idp/ArtifactResolutionService.php
index ac4592d615165ec924ab3ae3ba0784288a9c991d..3b674b31552355ef868a8730178d2ff287326e4c 100644
--- a/www/saml2/idp/ArtifactResolutionService.php
+++ b/www/saml2/idp/ArtifactResolutionService.php
@@ -51,4 +51,5 @@ $artifactResponse = new SAML2_ArtifactResponse();
 $artifactResponse->setIssuer($idpEntityId);
 $artifactResponse->setInResponseTo($request->getId());
 $artifactResponse->setAny($responseXML);
+sspmod_saml_Message::addSign($idpMetadata, NULL, $artifactResponse);
 $binding->send($artifactResponse);