diff --git a/builtin/builtin.js b/builtin/builtin.js
index f38db67..bf1145c 100644
--- a/builtin/builtin.js
+++ b/builtin/builtin.js
@@ -1,7 +1,8 @@
 /* START builtins */
 
 function _printf(msg) {
-  process.stdout.write(msg);
+  // Message is casted to string to prevent crash
+  process.stdout.write(msg.toString());
 }
 
 /* END builtins */
diff --git a/examples/playground.sb b/examples/playground.sb
index 502a6ee..6b9a030 100644
--- a/examples/playground.sb
+++ b/examples/playground.sb
@@ -1,6 +1,6 @@
 fn main() {
 
-    let arr = ["Foo", "Bar"]
+    let arr = [1, 2, 3]
 
     for x in arr {
         _printf(x)