diff --git a/lisp/progmodes/gdb-ui.el b/lisp/progmodes/gdb-ui.el
index 007033a87ba..be2b99c8975 100644
--- a/lisp/progmodes/gdb-ui.el
+++ b/lisp/progmodes/gdb-ui.el
@@ -312,7 +312,7 @@ Also display the main routine in the disassembly buffer if present."
   :version "22.1")
 
 (defcustom gdb-many-windows nil
-  "Nil means just pop up the GUD buffer unless `gdb-show-main' is t.
+  "nil means just pop up the GUD buffer unless `gdb-show-main' is t.
 In this case it starts with two windows: one displaying the GUD
 buffer and the other with the source file with the main routine
 of the debugged program.  Non-nil means display the layout shown for