diff --git a/lib/SAML2/HTTPArtifact.php b/lib/SAML2/HTTPArtifact.php
index 21646ff6469a2349aa15d0076048db47a630951d..f049272ccaa164d0b461d97069cd638e1f119d89 100644
--- a/lib/SAML2/HTTPArtifact.php
+++ b/lib/SAML2/HTTPArtifact.php
@@ -117,6 +117,11 @@ class SAML2_HTTPArtifact extends SAML2_Binding {
 		}
 
 		$xml = $artifactResponse->getAny();
+		if ($xml === NULL) {
+			/* Empty ArtifactResponse - possibly because of Artifact replay? */
+			return NULL;
+		}
+
 		$samlresponse = SAML2_Message::fromXML($xml);
 		$samlresponse->addValidator(array(get_class($this), 'validateSignature'), $artifactResponse);