diff --git a/src/AuthenticationResponseValidatorBuilder.php b/src/AuthenticationResponseValidatorBuilder.php
index e76b89b..22b37a2 100644
--- a/src/AuthenticationResponseValidatorBuilder.php
+++ b/src/AuthenticationResponseValidatorBuilder.php
@@ -44,6 +44,7 @@ public function getTrustedCaCertificates()
     public function withTrustedCaCertificatesFolder(string $trustedCertsPath) : AuthenticationResponseValidatorBuilder
     {
         foreach (array_diff(scandir($trustedCertsPath), array('.', '..')) as $file) {
+            if (!is_file($trustedCertsPath.$file)) continue;
             $caCertificate = file_get_contents($trustedCertsPath.$file);
             $caCert = Certificate::fromPEM(PEM::fromString($caCertificate));
             $this->trustedCaCertificates[] = $caCert;