diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index 23fd9122..4acc996d 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -430,6 +430,7 @@ Forth:
   color: "#341708"
   lexer: Text only
   extensions:
+  - .4th
   - .forth
   - .fth