diff --git a/Installation.md b/Installation.md
index 4764e74..7b69ffc 100644
--- a/Installation.md
+++ b/Installation.md
@@ -19,7 +19,8 @@ XenForo guide: [Click here](https://gitlab.com/ruany/litebans-php/wikis/Xenforo)
 ## Customization
 
 The web interface can be customized by changing the Bootstrap theme (inc/css/bootstrap.min.css).
-You can find Bootstrap themes at https://bootswatch.com/.
+You can find Bootstrap 4 themes at https://bootswatch.com/.
+Currently the web interface uses Bootstrap 4. Previous versions of litebans-php used Bootstrap 3. These Bootstrap versions are not forward-compatible nor reverse-compatible, so don't use old themes or everything will break.
 
 You can also try the [Material Design Theme](https://spigotmc.org/resources/46648) by [@ItsMeGlare](https://www.spigotmc.org/members/477275).