diff --git a/src/lib.rs b/src/lib.rs
index d7f174b..8e4c9f3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -258,7 +258,9 @@ pub struct Relation {
 
 #[derive(Debug, RustcDecodable, RustcEncodable, Clone, Copy, PartialEq, Eq)]
 pub enum RelationKind {
-    Impl,
+    Impl {
+        id: u32,
+    },
     SuperTrait,
 }