diff --git a/lib/SimpleSAML/Utils/HTTP.php b/lib/SimpleSAML/Utils/HTTP.php
index 257fdb57a38a65b9edfe4892c027d950d8e6189c..cb0bb41c693d6e12766f3feb129519572364cabd 100644
--- a/lib/SimpleSAML/Utils/HTTP.php
+++ b/lib/SimpleSAML/Utils/HTTP.php
@@ -139,7 +139,7 @@ class HTTP
             return false;
         }
         $scheme = parse_url($url, PHP_URL_SCHEME);
-        if ($scheme !== false && in_array(strtolower($scheme), ['http', 'https'], true)) {
+        if (is_string($scheme) && in_array(strtolower($scheme), ['http', 'https'], true)) {
             return true;
         }
         return false;