diff --git a/lib/SimpleSAML/XHTML/Template.php b/lib/SimpleSAML/XHTML/Template.php
index 74f85e63115163d4d7f9678a8740e16533af0f5c..3f9dbdc1373d9d00752d2996b3791a06a61b399b 100644
--- a/lib/SimpleSAML/XHTML/Template.php
+++ b/lib/SimpleSAML/XHTML/Template.php
@@ -120,7 +120,7 @@ class Template
         // check if we need to attach a theme controller
         $controller = $this->configuration->getString('theme.controller', false);
         if ($controller && class_exists($controller) &&
-            class_implements($controller, '\SimpleSAML\XHTML\TemplateControllerInterface')
+            in_array('\SimpleSAML\XHTML\TemplateControllerInterface', class_implements($controller))
         ) {
             $this->controller = new $controller();
         }