diff --git a/lib/handlers_v5.js b/lib/handlers_v5.js
index a15d0af..8e2e889 100755
--- a/lib/handlers_v5.js
+++ b/lib/handlers_v5.js
@@ -84,7 +84,7 @@ function kernel_info_request(request) {
                 "name": "javascript",
                 "version": nodeVersion,
                 "mimetype": "application/javascript",
-                "file_extension": "js",
+                "file_extension": ".js",
             },
             "banner": (
                 "IJavascript v" + ijsVersion + "\n" +