diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index 7350bb2a..a0744c92 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -1698,6 +1698,8 @@ R:
   extensions:
   - .r
   - .R
+  - .Rd
+  - .rd
   - .rsx
   filenames:
   - .Rprofile