diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index 79a1d517..270f1291 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -166,6 +166,8 @@ C#:
   aliases:
   - csharp
   primary_extension: .cs
+  extensions:
+  - .csx
 
 C++:
   type: programming