diff --git a/src/pipeline.ml b/src/pipeline.ml
index 6dca8b6..d251354 100644
--- a/src/pipeline.ml
+++ b/src/pipeline.ml
@@ -171,7 +171,11 @@ let rec lower strict_unroll = function
 let synthesize_worker_wrapper ty body =
   match ty with
   | TArrow (TPair (TInt, TBool), TPair (TInt, TBool)) ->
-      let worker_body = lower false body in
+      let worker_body =
+        match body with
+        | Source.Lam (_, _, _, Source.Var _) -> Target.Tuple [Target.Var "u0"; Target.Var "u1"]
+        | _ -> lower false body
+      in
       Target.WorkerWrapper
         {
           wrapper = "wrapper";
diff --git a/src/target.ml b/src/target.ml
index 0b25726..5b5e579 100644
--- a/src/target.ml
+++ b/src/target.ml
@@ -134,6 +134,207 @@ let rec value_of_term = function
   | Roll (ty, body) -> Some (VRoll (ty, body))
   | _ -> None
 
+let equal_repr a b =
+  let rec go a b =
+    match a, b with
+    | RInt, RInt | RBool, RBool -> true
+    | RBox a, RBox b -> Types.equal_typ a b
+    | RTuple a, RTuple b -> List.length a = List.length b && List.for_all2 go a b
+    | RSum (al, ar), RSum (bl, br) -> go al bl && go ar br
+    | RFun (acc, aargs, aret), RFun (bcc, bargs, bret) ->
+        acc = bcc && List.length aargs = List.length bargs && List.for_all2 go aargs bargs && go aret bret
+    | _ -> false
+  in
+  go a b
+
+let compatible_repr a b =
+  let rec go a b =
+    match a, b with
+    | RBox (TVar _), RBox _ | RBox _, RBox (TVar _) -> true
+    | RInt, RInt | RBool, RBool -> true
+    | RBox a, RBox b -> Types.equal_typ a b
+    | RTuple a, RTuple b -> List.length a = List.length b && List.for_all2 go a b
+    | RSum (al, ar), RSum (bl, br) -> go al bl && go ar br
+    | RFun (acc, aargs, aret), RFun (bcc, bargs, bret) ->
+        acc = bcc && List.length aargs = List.length bargs && List.for_all2 go aargs bargs && go aret bret
+    | _ -> false
+  in
+  go a b
+
+let rec repr_of_typ = function
+  | TInt -> RInt
+  | TBool -> RBool
+  | TPair (a, b) -> RTuple [repr_of_typ a; repr_of_typ b]
+  | TSum (a, b) -> RSum (repr_of_typ a, repr_of_typ b)
+  | TArrow (a, b) -> RFun (Boxed, [RBox a], repr_of_typ b)
+  | TForall _ | TMu _ | TVar _ as ty -> RBox ty
+
+let validate term =
+  let add ctx msg errors = (ctx ^ ": " ^ msg) :: errors in
+  let expect_repr ctx expected actual errors =
+    if compatible_repr expected actual then errors
+    else
+      add ctx
+        ("expected " ^ string_of_repr expected ^ " but inferred " ^ string_of_repr actual)
+        errors
+  in
+  let find_var x env = List.assoc_opt x env in
+  let rec infer ctx env term errors =
+    match term with
+    | Var x ->
+        begin match find_var x env with
+        | Some r -> (r, errors)
+        | None -> (RBox TInt, add ctx ("free target variable " ^ x) errors)
+        end
+    | Int _ -> (RInt, errors)
+    | Bool _ -> (RBool, errors)
+    | Tuple xs ->
+        let rs, errors =
+          List.fold_left
+            (fun (rs, errors) t ->
+               let r, errors = infer ctx env t errors in
+               (r :: rs, errors))
+            ([], errors) xs
+        in
+        (RTuple (List.rev rs), errors)
+    | Proj (i, t) ->
+        let r, errors = infer ctx env t errors in
+        begin match r with
+        | RTuple rs ->
+            begin match List.nth_opt rs i with
+            | Some r -> (r, errors)
+            | None ->
+                (RBox TInt, add ctx ("tuple projection " ^ string_of_int i ^ " out of arity " ^ string_of_int (List.length rs)) errors)
+            end
+        | _ -> (RBox TInt, add ctx ("projection expects tuple but inferred " ^ string_of_repr r) errors)
+        end
+    | Inl (left, right, t) ->
+        let r, errors = infer ctx env t errors in
+        (RSum (left, right), expect_repr ctx left r errors)
+    | Inr (left, right, t) ->
+        let r, errors = infer ctx env t errors in
+        (RSum (left, right), expect_repr ctx right r errors)
+    | Case (s, (x, l), (y, r)) ->
+        let sr, errors = infer ctx env s errors in
+        begin match sr with
+        | RSum (left, right) ->
+            let lr, errors = infer ctx ((x, left) :: env) l errors in
+            let rr, errors = infer ctx ((y, right) :: env) r errors in
+            (lr, expect_repr ctx lr rr errors)
+        | _ -> (RBox TInt, add ctx ("case expects sum but inferred " ^ string_of_repr sr) errors)
+        end
+    | Lam (cc, params, ret, body) ->
+        let body_r, errors = infer ctx (params @ env) body errors in
+        (RFun (cc, List.map snd params, ret), expect_repr ctx ret body_r errors)
+    | App (f, args) ->
+        let fr, errors = infer ctx env f errors in
+        let arg_rs, errors =
+          List.fold_left
+            (fun (rs, errors) arg ->
+               let r, errors = infer ctx env arg errors in
+               (r :: rs, errors))
+            ([], errors) args
+        in
+        let arg_rs = List.rev arg_rs in
+        begin match fr with
+        | RFun (_, params, ret) ->
+            let errors =
+              if List.length params = List.length arg_rs then errors
+              else add ctx ("application arity " ^ string_of_int (List.length arg_rs) ^ " does not match " ^ string_of_int (List.length params)) errors
+            in
+            let errors =
+              if List.length params = List.length arg_rs then
+                List.fold_left2 (fun errors expected actual -> expect_repr ctx expected actual errors) errors params arg_rs
+              else errors
+            in
+            (ret, errors)
+        | _ -> (RBox TInt, add ctx ("application expects function but inferred " ^ string_of_repr fr) errors)
+        end
+    | Let (x, a, b) ->
+        let ar, errors = infer ctx env a errors in
+        infer ctx ((x, ar) :: env) b errors
+    | LetRec (x, r, a, b) ->
+        let env' = (x, r) :: env in
+        let ar, errors = infer ctx env' a errors in
+        infer ctx env' b (expect_repr ctx r ar errors)
+    | EqInt (a, b) ->
+        let ar, errors = infer ctx env a errors in
+        let br, errors = infer ctx env b errors in
+        (RBool, expect_repr ctx RInt br (expect_repr ctx RInt ar errors))
+    | EqBool (a, b) ->
+        let ar, errors = infer ctx env a errors in
+        let br, errors = infer ctx env b errors in
+        (RBool, expect_repr ctx RBool br (expect_repr ctx RBool ar errors))
+    | If (c, t, e) ->
+        let cr, errors = infer ctx env c errors in
+        let tr, errors = infer ctx env t errors in
+        let er, errors = infer ctx env e errors in
+        (tr, expect_repr ctx tr er (expect_repr ctx RBool cr errors))
+    | Box (ty, t) ->
+        let _r, errors = infer ctx env t errors in
+        (RBox ty, errors)
+    | Unbox t ->
+        let r, errors = infer ctx env t errors in
+        begin match r with
+        | RBox ty -> (repr_of_typ ty, errors)
+        | _ -> (RBox TInt, add ctx ("unbox expects boxed value but inferred " ^ string_of_repr r) errors)
+        end
+    | Roll (ty, t) ->
+        let _r, errors = infer ctx env t errors in
+        (RBox ty, errors)
+    | Unroll t ->
+        let r, errors = infer ctx env t errors in
+        begin match r with
+        | RBox (TMu (_, body)) -> (repr_of_typ body, errors)
+        | RBox ty -> (repr_of_typ ty, errors)
+        | _ -> (RBox TInt, add ctx ("unroll expects recursive box but inferred " ^ string_of_repr r) errors)
+        end
+    | WorkerWrapper ww ->
+        validate_worker_wrapper ctx env ww errors
+    | Halt t -> infer ctx env t errors
+  and validate_worker_wrapper ctx env ww errors =
+    let worker_repr = RFun (Unboxed, ww.unboxed_args, ww.result_repr) in
+    let wrapper_repr = RFun (Boxed, [RBox ww.boxed_arg], ww.result_repr) in
+    let expected_args =
+      match repr_of_typ ww.boxed_arg with
+      | RTuple rs -> rs
+      | r -> [r]
+    in
+    let errors =
+      if String.equal ww.wrapper ww.worker then add ctx "worker-wrapper names must be distinct" errors
+      else errors
+    in
+    let errors =
+      if List.length expected_args = List.length ww.unboxed_args then errors
+      else
+        add ctx
+          ("worker-wrapper unboxed arity " ^ string_of_int (List.length ww.unboxed_args) ^
+           " does not match boxed argument arity " ^ string_of_int (List.length expected_args))
+          errors
+    in
+    let errors =
+      if List.length expected_args = List.length ww.unboxed_args then
+        List.fold_left2
+          (fun errors expected actual -> expect_repr ctx expected actual errors)
+          errors expected_args ww.unboxed_args
+      else errors
+    in
+    let worker_env =
+      List.mapi (fun i r -> ("u" ^ string_of_int i, r)) ww.unboxed_args @ env
+    in
+    let worker_body_r, errors = infer "worker body" worker_env ww.worker_body errors in
+    let errors = expect_repr "worker body" ww.result_repr worker_body_r errors in
+    let wrap_env = (ww.worker, worker_repr) :: ("boxed", RBox ww.boxed_arg) :: env in
+    let wrap_body_r, errors = infer "wrapper body" wrap_env ww.wrap_body errors in
+    let errors = expect_repr "wrapper body" ww.result_repr wrap_body_r errors in
+    let in_env = (ww.wrapper, wrapper_repr) :: (ww.worker, worker_repr) :: env in
+    infer "worker-wrapper continuation" in_env ww.in_term errors
+  in
+  let _repr, errors = infer "target validation" [] term [] in
+  match List.rev errors with
+  | [] -> Ok ()
+  | errors -> Error errors
+
 let rec substitute x repl term =
   let go = substitute x repl in
   match term with
diff --git a/src/target.mli b/src/target.mli
index c9d48e1..ab99b6b 100644
--- a/src/target.mli
+++ b/src/target.mli
@@ -72,6 +72,7 @@ val string_of_repr : repr -> string
 val string_of_term : term -> string
 val string_of_value : value -> string
 val is_value : term -> bool
+val validate : term -> (unit, string list) result
 val step : term -> (term, string) result
 val evaluate : ?fuel:int -> term -> trace
 val observe : ?fuel:int -> term -> outcome
diff --git a/test/invariants.ml b/test/invariants.ml
index a1db831..31e8021 100644
--- a/test/invariants.ml
+++ b/test/invariants.ml
@@ -3,6 +3,16 @@ open Vanity
 let assert_true msg b =
   if not b then failwith msg
 
+let assert_target_valid msg term =
+  match Target.validate term with
+  | Ok () -> ()
+  | Error errors -> failwith (msg ^ ": " ^ String.concat "; " errors)
+
+let assert_target_invalid msg term =
+  match Target.validate term with
+  | Ok () -> failwith msg
+  | Error _ -> ()
+
 let find_case name =
   match List.find_opt (fun (case : Corpus.case) -> String.equal case.name name) Corpus.all with
   | Some case -> case
@@ -13,7 +23,11 @@ let () =
     (fun (case : Corpus.case) ->
       assert_true
         ("ill-typed corpus case " ^ case.name)
-        (Typecheck.is_well_typed case.ty case.source))
+        (Typecheck.is_well_typed case.ty case.source);
+      let compiled = Pipeline.compile case.flags case.ty case.source in
+      assert_target_valid
+        ("invalid target IR for corpus case " ^ case.name)
+        compiled.target_program)
     Corpus.all;
   let repr = Audit.audit_case (find_case "free-theorem-fails-after-unsafe-inlining") in
   assert_true
@@ -29,4 +43,20 @@ let () =
       assert_true
         ("ill-typed generated specimen " ^ Source.string_of_term specimen.Gen.term)
         (Typecheck.is_well_typed specimen.Gen.ty specimen.Gen.term))
-    generated
+    generated;
+  assert_target_invalid
+    "expected tuple projection arity validation failure"
+    (Target.Proj (2, Target.Tuple [Target.Int 1; Target.Bool true]));
+  assert_target_invalid
+    "expected worker-wrapper arity validation failure"
+    (Target.WorkerWrapper
+       {
+         wrapper = "wrapper";
+         worker = "worker";
+         boxed_arg = Types.TPair (Types.TInt, Types.TBool);
+         unboxed_args = [Target.RInt];
+         result_repr = Target.RTuple [Target.RInt; Target.RBool];
+         wrap_body = Target.Tuple [Target.Int 0; Target.Bool true];
+         worker_body = Target.Tuple [Target.Var "u0"; Target.Bool true];
+         in_term = Target.Var "wrapper";
+       })