1 files changed, 6 insertions, 1 deletions
diff --git a/compiler/rustc_middle/src/mir/interpret/error.rs b/compiler/rustc_middle/src/mir/interpret/error.rs
index 2b0cfb86564..3e895c6b280 100644
--- a/compiler/rustc_middle/src/mir/interpret/error.rs
+++ b/compiler/rustc_middle/src/mir/interpret/error.rs
@@ -426,7 +426,12 @@ pub enum UndefinedBehaviorInfo<'tcx> {
     /// Trying to set discriminant to the niched variant, but the value does not match.
     InvalidNichedEnumVariantWritten { enum_ty: Ty<'tcx> },
     /// ABI-incompatible argument types.
-    AbiMismatchArgument { caller_ty: Ty<'tcx>, callee_ty: Ty<'tcx> },
+    AbiMismatchArgument {
+        /// The index of the argument whose type is wrong.
+        arg_idx: usize,
+        caller_ty: Ty<'tcx>,
+        callee_ty: Ty<'tcx>,
+    },
     /// ABI-incompatible return types.
     AbiMismatchReturn { caller_ty: Ty<'tcx>, callee_ty: Ty<'tcx> },
 }