diff --git a/rmp/src/value.rs b/rmp/src/value.rs
index b6ccca05..e490989f 100644
--- a/rmp/src/value.rs
+++ b/rmp/src/value.rs
@@ -77,7 +77,9 @@ impl ::std::fmt::Display for Value {
 
                 write!(f, "}}")
             }
-            _ => unimplemented!()
+            Value::Ext(ty, ref data) => {
+                write!(f, "[{}, {:?}]", ty, data)
+            }
         }
     }
 }
diff --git a/rmp/tests/value.rs b/rmp/tests/value.rs
index 090b6ddb..c5de96c2 100644
--- a/rmp/tests/value.rs
+++ b/rmp/tests/value.rs
@@ -51,3 +51,10 @@ fn display_map() {
     assert_eq!("{nil: nil, true: false}", format!("{}", Value::Map(vec![(Value::Nil, Value::Nil),
         (Value::Boolean(true), Value::Boolean(false))])));
 }
+
+#[test]
+fn display_ext() {
+    assert_eq!("[1, []]", format!("{}", Value::Ext(1, vec![])));
+    assert_eq!("[1, [100]]", format!("{}", Value::Ext(1, vec![100])));
+    assert_eq!("[1, [100, 42]]", format!("{}", Value::Ext(1, vec![100, 42])));
+}