diff --git a/.dir-locals.el b/.dir-locals.el
index 572a35f828..adcc50c560 100644
--- a/.dir-locals.el
+++ b/.dir-locals.el
@@ -3,6 +3,7 @@
 ((nil
   . ((fill-column . 78)
      (tab-width   .  8)
+     (sentence-end-double-space . t)
 
      ;; For use with 'bug-reference-prog-mode'.
      (bug-reference-url-format . "http://bugs.gnu.org/%s")