diff --git a/serde/src/de/mod.rs b/serde/src/de/mod.rs
index ae5d04f4..2be58104 100644
--- a/serde/src/de/mod.rs
+++ b/serde/src/de/mod.rs
@@ -68,7 +68,7 @@ pub enum Type {
 
 ///////////////////////////////////////////////////////////////////////////////
 
-pub trait Deserialize {
+pub trait Deserialize: Sized {
     /// Deserialize this value given this `Deserializer`.
     fn deserialize<D>(deserializer: &mut D) -> Result<Self, D::Error>
         where D: Deserializer;