diff --git a/composer.json b/composer.json
index d545129..243e148 100644
--- a/composer.json
+++ b/composer.json
@@ -28,4 +28,4 @@
     "archive": {
         "exclude": ["/example", "/tests"]
     }
-}
+}
\ No newline at end of file
diff --git a/src/Spid/Saml/In/Response.php b/src/Spid/Saml/In/Response.php
index b3738fe..1292a6f 100644
--- a/src/Spid/Saml/In/Response.php
+++ b/src/Spid/Saml/In/Response.php
@@ -57,8 +57,8 @@ public function validate($xml, $hasAssertion): bool
         } elseif ($xml->getElementsByTagName('Issuer')->item(0)->nodeValue != $_SESSION['idpEntityId']) {
             throw new \Exception("Invalid Issuer attribute, expected " . $_SESSION['idpEntityId'] .
                 " but received " . $xml->getElementsByTagName('Issuer')->item(0)->nodeValue);
-        } elseif ($xml->getElementsByTagName('Issuer')->item(0)->getAttribute('Format') !=
-            'urn:oasis:names:tc:SAML:2.0:nameid-format:entity') {
+        } elseif (!epmty($xml->getElementsByTagName('Issuer')->item(0)->getAttribute('Format')) && 
+                    $xml->getElementsByTagName('Issuer')->item(0)->getAttribute('Format') != 'urn:oasis:names:tc:SAML:2.0:nameid-format:entity') {
             throw new \Exception("Invalid Issuer attribute, expected 'urn:oasis:names:tc:SAML:2.0:nameid-format:" .
                 "entity'" . " but received " . $xml->getElementsByTagName('Issuer')->item(0)->getAttribute('Format'));
         }