diff --git a/sledge/src/llair/exp.ml b/sledge/src/llair/exp.ml
index bff555aeb..34ed8888f 100644
--- a/sledge/src/llair/exp.ml
+++ b/sledge/src/llair/exp.ml
@@ -366,7 +366,11 @@ let typ_of = function
 let typ = typ_of
 
 let type_check e typ =
-  assert (Option.for_all ~f:(Typ.castable typ) (typ_of e))
+  assert (
+    Option.for_all ~f:(Typ.castable typ) (typ_of e)
+    || fail "%a@ : %a not <:@ %a" pp e Typ.pp
+         (Option.value_exn (typ_of e))
+         Typ.pp typ )
 
 let type_check2 e f typ = type_check e typ ; type_check f typ
 
diff --git a/sledge/src/llair/frontend.ml b/sledge/src/llair/frontend.ml
index b59b87e31..e565fef93 100644
--- a/sledge/src/llair/frontend.ml
+++ b/sledge/src/llair/frontend.ml
@@ -532,7 +532,11 @@ and xlate_opcode : x -> Llvm.llvalue -> Llvm.Opcode.t -> Exp.t =
           [%Trace.call fun {pf} ->
             pf "%i %a" i pp_llvalue (Llvm.operand llv i)]
           ;
-          let idx = xlate_rand i in
+          let idx =
+            Exp.convert ~dst:Typ.siz
+              ~src:(xlate_type x (Llvm.type_of (Llvm.operand llv i)))
+              (xlate_rand i)
+          in
           ( if i = 1 then
             let base = xlate_rand 0 in
             let lltyp = Llvm.type_of (Llvm.operand llv 0) in