diff --git a/.dir-locals.el b/.dir-locals.el
index 1ac9c993d28122bd1bc5aeabef72211b10354ccb..2fdad78217b612e268ab312823734459e62fb70f 100644
--- a/.dir-locals.el
+++ b/.dir-locals.el
@@ -1,6 +1,8 @@
 ((c-mode . ((indent-tabs-mode . nil)
+            (fill-column . 100)
             (c-file-style . "gnu")))
  (c++-mode . ((indent-tabs-mode . nil)
+              (fill-column . 100)
               (c-file-style . "gnu")))
  (makefile-mode . ((indent-tabs-mode . t)))
  (octave-mode . ((indent-tabs-mode . nil)