diff --git a/lib/SimpleSAML/Metadata/SAMLParser.php b/lib/SimpleSAML/Metadata/SAMLParser.php
index fc84e911dc3427bbed8a34512c0776217df7c561..7820bb15b8e4bd13deb22062e7e3738c374acd57 100644
--- a/lib/SimpleSAML/Metadata/SAMLParser.php
+++ b/lib/SimpleSAML/Metadata/SAMLParser.php
@@ -1162,6 +1162,9 @@ class SimpleSAML_Metadata_SAMLParser {
 	 * @return TRUE if it was signed with the certificate with the given fingerprint, FALSE otherwise.
 	 */
 	public function validateFingerprint($fingerprint) {
+		assert('is_string($fingerprint)');
+
+		$fingerprint = strtolower(str_replace(":", "", $fingerprint));
 
 		foreach ($this->validators as $validator) {
 			foreach ($validator->getValidatingCertificates() as $cert) {