diff --git a/src/libsyntax/opt_vec.rs b/src/libsyntax/opt_vec.rs
index 2d7801a22de..46940d2d4da 100644
--- a/src/libsyntax/opt_vec.rs
+++ b/src/libsyntax/opt_vec.rs
@@ -140,6 +140,10 @@ impl<A:Eq> Eq for OptVec<A> {
     }
 }
 
+impl<T> Default for OptVec<T> {
+    fn default() -> OptVec<T> { Empty }
+}
+
 pub struct OptVecIterator<'self, T> {
     priv iter: Option<VecIterator<'self, T>>
 }