diff --git a/.dir-locals.el b/.dir-locals.el
index 148e4ca61f0..be19e29a5ab 100644
--- a/.dir-locals.el
+++ b/.dir-locals.el
@@ -1 +1,3 @@
-((c-mode . ((c-basic-offset . 3))))
+((c-mode . ((c-basic-offset . 3)))
+ (c++-mode . ((c-basic-offset . 3)))
+)