diff --git a/src/base.rs b/src/base.rs
index 912338e048b..63c499d4855 100644
--- a/src/base.rs
+++ b/src/base.rs
@@ -774,7 +774,7 @@ fn is_fat_ptr<'tcx>(fx: &FunctionCx<'_, '_, 'tcx>, ty: Ty<'tcx>) -> bool {
                             let variant_dest = lval.downcast_variant(fx, variant_index);
                             (variant_index, variant_dest, active_field_index)
                         }
-                        _ => (VariantIdx::from_u32(0), lval, None),
+                        _ => (FIRST_VARIANT, lval, None),
                     };
                     if active_field_index.is_some() {
                         assert_eq!(operands.len(), 1);
diff --git a/src/lib.rs b/src/lib.rs
index bed79859f51..1bd03403f24 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -86,7 +86,7 @@ mod prelude {
         self, FloatTy, Instance, InstanceDef, IntTy, ParamEnv, Ty, TyCtxt, TypeAndMut,
         TypeFoldable, TypeVisitableExt, UintTy,
     };
-    pub(crate) use rustc_target::abi::{Abi, Scalar, Size, VariantIdx};
+    pub(crate) use rustc_target::abi::{Abi, Scalar, Size, VariantIdx, FIRST_VARIANT};
 
     pub(crate) use rustc_data_structures::fx::FxHashMap;
 
diff --git a/src/unsize.rs b/src/unsize.rs
index ecf187a0b0f..93eefd92342 100644
--- a/src/unsize.rs
+++ b/src/unsize.rs
@@ -146,7 +146,7 @@ pub(crate) fn coerce_unsized_into<'tcx>(
         (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
             assert_eq!(def_a, def_b);
 
-            for i in 0..def_a.variant(VariantIdx::new(0)).fields.len() {
+            for i in 0..def_a.variant(FIRST_VARIANT).fields.len() {
                 let src_f = src.value_field(fx, mir::Field::new(i));
                 let dst_f = dst.place_field(fx, mir::Field::new(i));