diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index dc4ce94b44..2efe1a5b46 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -4318,6 +4318,7 @@ Markdown:
   - ".ronn"
   - ".scd"
   - ".workbook"
+  - ".mdc"
   filenames:
   - contents.lr
   tm_scope: text.md