diff --git a/library/Icinga/Web/Navigation/Navigation.php b/library/Icinga/Web/Navigation/Navigation.php
index 8cf3f6845..85460aff3 100644
--- a/library/Icinga/Web/Navigation/Navigation.php
+++ b/library/Icinga/Web/Navigation/Navigation.php
@@ -380,7 +380,7 @@ class Navigation implements ArrayAccess, Countable, IteratorAggregate
                     $name = $item->getName();
                     do {
                         if (preg_match('~_(\d+)$~', $name, $matches)) {
-                            $name = preg_replace('~_\d+$~', $matches[1] + 1, $name);
+                            $name = preg_replace('~_\d+$~', (int) $matches[1] + 1, $name);
                         } else {
                             $name .= '_2';
                         }