diff --git a/Module:-xwindow.md b/Module:-xwindow.md
index 7a64fd7..7a86190 100644
--- a/Module:-xwindow.md
+++ b/Module:-xwindow.md
@@ -1,5 +1,7 @@
 This module show the title of the currently focused window.
 
+**NOTE**: Requires a WM that supports the EWMH atom _NET_ACTIVE_DESKTOP.
+
 ### Basic settings
   ~~~ ini
   [module/title]