diff --git a/src/Knp/Menu/Twig/MenuExtension.php b/src/Knp/Menu/Twig/MenuExtension.php
index 9829cfe0..3fc3df3d 100644
--- a/src/Knp/Menu/Twig/MenuExtension.php
+++ b/src/Knp/Menu/Twig/MenuExtension.php
@@ -150,6 +150,6 @@ public function isAncestor(ItemInterface $item, ?int $depth = null): bool
 
     public function spaceless(string $content): string
     {
-        return trim(preg_replace('/>\s+</', '><', $content));
+        return trim((string) preg_replace('/>\s+</', '><', $content));
     }
 }