diff --git a/stable/xdg-shell/xdg-shell.xml b/stable/xdg-shell/xdg-shell.xml
index 7fecaa8..c98ea68 100644
--- a/stable/xdg-shell/xdg-shell.xml
+++ b/stable/xdg-shell/xdg-shell.xml
@@ -205,6 +205,7 @@
 	'bottom_right'), the anchor point will be at the specified corner;
 	otherwise, the derived anchor point will be centered on the specified
 	edge, or in the center of the anchor rectangle if no edge is specified.
+	If the anchor is not in the ‘anchor’ enum, an invalid_input error is raised.
       </description>
       <arg name="anchor" type="uint" enum="anchor"
 	   summary="anchor point"/>