diff --git a/doc/usage/theming.rst b/doc/usage/theming.rst
index 60bc20e24fb..f6a9460ec1d 100644
--- a/doc/usage/theming.rst
+++ b/doc/usage/theming.rst
@@ -127,6 +127,10 @@ Builtin themes
 
 Sphinx comes with a selection of themes to choose from.
 
+Note that from these themes only the Alabaster and Scrolls themes are
+mobile-optimated, the other themes resort to horizontal scrolling
+if the screen is too narrow.
+
 .. cssclass:: clear
 
 These themes are: