diff --git a/languages.json b/languages.json
index 4ff4b39c7..97f741966 100644
--- a/languages.json
+++ b/languages.json
@@ -578,7 +578,7 @@
       "quotes": [["\\\"", "\\\""]],
       "line_comment": ["//"],
       "multi_line_comments": [["(*", "*)"]],
-      "extensions": ["fst"]
+      "extensions": ["fst", "fsti"]
     },
     "Futhark": {
       "line_comment": ["--"],