diff --git a/src/librustc/mir/mod.rs b/src/librustc/mir/mod.rs
index f244306a0cf4..1d0e95245ea2 100644
--- a/src/librustc/mir/mod.rs
+++ b/src/librustc/mir/mod.rs
@@ -888,7 +888,7 @@ impl<'tcx> Lvalue<'tcx> {
         self.elem(ProjectionElem::Deref)
     }
 
-    pub fn downcast(self, adt_def: AdtDef<'tcx>, variant_index: usize) -> Lvalue<'tcx> {
+    pub fn downcast(self, adt_def: &'tcx AdtDef, variant_index: usize) -> Lvalue<'tcx> {
         self.elem(ProjectionElem::Downcast(adt_def, variant_index))
     }