diff --git a/lispref/keymaps.texi b/lispref/keymaps.texi
index 8dfd2db8dfc..c087b968793 100644
--- a/lispref/keymaps.texi
+++ b/lispref/keymaps.texi
@@ -333,7 +333,7 @@ new parent keymaps that reflect what @var{parent} specifies for those
 prefix keys.
 @end defun
 
-Here is an example showing how to make a keymap that inherits
+   Here is an example showing how to make a keymap that inherits
 from @code{text-mode-map}:
 
 @example
@@ -342,6 +342,12 @@ from @code{text-mode-map}:
   map)
 @end example
 
+  A non-sparse keymap can have a parent too, but this is not very
+useful.  A non-sparse keymap always specifies something as the binding
+for every numeric character code without modifier bits, even if it is
+@code{nil}, so these character's bindings are never inherited from
+the parent keymap.
+
 @node Prefix Keys
 @section Prefix Keys
 @cindex prefix key