diff --git a/vars/medium.localvars b/vars/medium.localvars
index 5b17d62b6..fbf489737 100644
--- a/vars/medium.localvars
+++ b/vars/medium.localvars
@@ -113,6 +113,9 @@ samba_enabled: False
 
 # 6-GENERIC-APPS
 
+# WARNING: CALIBRE REQUIRES X WINDOWS / OPENGL LIBRARIES.
+# Consider installing an OS that includes a GUI (desktop) environment.
+
 calibre_install: True
 calibre_enabled: True
 # Change calibre_port to 8010 if you're using XO laptops needing above idmgr