diff --git a/lisp/gnus/gnus-sum.el b/lisp/gnus/gnus-sum.el
index a39af45e92e..2391bd497ce 100644
--- a/lisp/gnus/gnus-sum.el
+++ b/lisp/gnus/gnus-sum.el
@@ -203,9 +203,10 @@ Useful functions to put in this list include:
 
 (defcustom gnus-build-sparse-threads nil
   "If non-nil, fill in the gaps in threads.
-If `some', only fill in the gaps that are needed to tie loose threads
-together.  If `more', fill in all leaf nodes that Gnus can find.  If
-non-nil and non-`some', fill in all gaps that Gnus manages to guess."
+If set to the symbol `some', only fill in the gaps that are
+needed to tie loose threads together.  If the symbol `more', fill
+in all leaf nodes that Gnus can find.  If t (or any other value),
+fill in all gaps that Gnus manages to guess."
   :group 'gnus-thread
   :type '(choice (const :tag "off" nil)
 		 (const some)