diff --git a/demos/03_demo.md b/demos/03_demo.md
index fbc8497056c3af72b25786f1675bdd88621300c1..17a73a7c6d4581af6c0a07757cd69e123d44061d 100644
--- a/demos/03_demo.md
+++ b/demos/03_demo.md
@@ -1,4 +1,4 @@
-```
+```ruby
 func changeB(a:String, b: inout String) {
    b = "\(a)\(b)"
 }
@@ -95,3 +95,4 @@ switch sr {
 	print("default")
 }
 ```
+{: .language-go}