diff --git a/rustbyexample/hello/testcase_list.rs b/rustbyexample/hello/testcase_list.rs
index 2f29761..263da30 100644
--- a/rustbyexample/hello/testcase_list.rs
+++ b/rustbyexample/hello/testcase_list.rs
@@ -8,9 +8,11 @@ impl fmt::Display for List {
 
         write!(f, "[")?;
 
-        for (count, v ) in vec.iter().enumerate() {
-            if count != 0 { write!(f, ", ")?; }
-            write!(f, "{}", v)?;
+        for (count, v) in vec.iter().enumerate() {
+            if count != 0 {
+                write!(f, ", ")?;
+            }
+            write!(f, "{}: {}", count, v)?;
         }
 
         write!(f, "]")