diff --git a/library/Icinga/File/Ini/IniEditor.php b/library/Icinga/File/Ini/IniEditor.php
index ebac0ceb6..85d71b697 100644
--- a/library/Icinga/File/Ini/IniEditor.php
+++ b/library/Icinga/File/Ini/IniEditor.php
@@ -493,7 +493,7 @@ class IniEditor
     private function isPropertyDeclaration($lineContent, array $key)
     {
         return preg_match(
-            '/^\s*' . preg_quote($this->formatKey($key)) . '\s*=\s*/',
+            '/^\s*' . preg_quote($this->formatKey($key), '/') . '\s*=\s*/',
             $lineContent
         ) === 1;
     }