diff --git a/lib/SimpleSAML/XML/Validator.php b/lib/SimpleSAML/XML/Validator.php
index ddd404b28e905b45f847f1efe3ccf4a4a9368b24..fef30bddb0caa804860198212382f5de0bdf40ac 100644
--- a/lib/SimpleSAML/XML/Validator.php
+++ b/lib/SimpleSAML/XML/Validator.php
@@ -86,7 +86,7 @@ class SimpleSAML_XML_Validator {
 		}
 
 		/* Load the key data. */
-		if (array_key_exists('PEM', $publickey)) {
+		if ($publickey !== FALSE && array_key_exists('PEM', $publickey)) {
 			/* We have PEM data for the public key / certificate. */
 			$objKey->loadKey($publickey['PEM']);
 		} else {