diff --git a/lib/SimpleSAML/Metadata/SAMLBuilder.php b/lib/SimpleSAML/Metadata/SAMLBuilder.php
index dfe487ff1088f057beb13e089d5d2e135d60f255..8092f85782a1b97c76fa6c65cb7cd559a74c8839 100644
--- a/lib/SimpleSAML/Metadata/SAMLBuilder.php
+++ b/lib/SimpleSAML/Metadata/SAMLBuilder.php
@@ -604,6 +604,7 @@ class SimpleSAML_Metadata_SAMLBuilder {
 		$certData = $certInfo['certData'];
 
 		$keyDescriptor = $this->createElement('KeyDescriptor');
+		$keyDescriptor->setAttribute('use', 'signing');
 		$ssoDesc->appendChild($keyDescriptor);
 
 		$keyInfo = $this->document->createElementNS('http://www.w3.org/2000/09/xmldsig#', 'ds:KeyInfo');