diff --git a/lisp/simple.el b/lisp/simple.el
index bec0d9ed5f3..1554378d138 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -3093,7 +3093,7 @@ START and END specify the portion of the current buffer to be copied."
 (defvar activate-mark-hook nil
   "Hook run when the mark becomes active.
 It is also run at the end of a command, if the mark is active and
-it is possible that the region may have changed")
+it is possible that the region may have changed.")
 
 (defvar deactivate-mark-hook nil
   "Hook run when the mark becomes inactive.")