diff --git a/src/main/resources/io/jenkins/plugins/thememanager/header/main.js b/src/main/resources/io/jenkins/plugins/thememanager/header/main.js
index 5a78749..828ce81 100644
--- a/src/main/resources/io/jenkins/plugins/thememanager/header/main.js
+++ b/src/main/resources/io/jenkins/plugins/thememanager/header/main.js
@@ -5,7 +5,7 @@
   if (theme.id && theme.id !== '') {
     document.documentElement.dataset.theme = theme.id
   }
-  window.isSystemRespectingTheme = themeJson.respect_system_appearance
+  window.isSystemRespectingTheme = theme.respect_system_appearance
 
   const propertiesJson = document.getElementById('theme-manager-properties').text
   const parsedProperties = JSON.parse(propertiesJson);