diff --git a/src/SAML2/Compat/ContainerSingleton.php b/src/SAML2/Compat/ContainerSingleton.php
index 167fa8664..c9094aa41 100644
--- a/src/SAML2/Compat/ContainerSingleton.php
+++ b/src/SAML2/Compat/ContainerSingleton.php
@@ -19,7 +19,7 @@ class ContainerSingleton
      */
     public static function getInstance() : AbstractContainer
     {
-        if (!self::$container) {
+        if (!isset(self::$container)) {
             self::$container = self::initSspContainer();
         }
         return self::$container;