diff --git a/serde_codegen/src/lib.rs b/serde_codegen/src/lib.rs
index 42e3a0c7..25a9fe03 100644
--- a/serde_codegen/src/lib.rs
+++ b/serde_codegen/src/lib.rs
@@ -169,8 +169,8 @@ macro_rules! shim {
             use syntax::parse;
             let name = stringify!($name).to_string();
             let cfg = Vec::new();
-            let sess = parse::ParseSess::new();
-            let impl_item = parse::parse_item_from_source_str(name, expanded, cfg, &sess);
+            let sess = cx.parse_sess;
+            let impl_item = parse::parse_item_from_source_str(name, expanded, cfg, sess);
             push(::syntax::ext::base::Annotatable::Item(impl_item.unwrap().unwrap()));
         }
     };