diff --git a/src/bin/expect_tests/contract_tests.ml b/src/bin/expect_tests/contract_tests.ml
index fc87bc8cb..53db85afc 100644
--- a/src/bin/expect_tests/contract_tests.ml
+++ b/src/bin/expect_tests/contract_tests.ml
@@ -924,3 +924,7 @@ let%expect_test _ =
                NIL operation ;
                PAIR ;
                DIP { DROP 2 } } } |}]
+
+let%expect_test _ =
+  run_ligo_bad [ "compile-contract" ; contract "bad_type_operator.ligo" ; "main" ] ;
+  [%expect {| ligo: bad type operator (TO_Map (unit,unit)): |}] ;
\ No newline at end of file
diff --git a/src/passes/2-simplify/cameligo.ml b/src/passes/2-simplify/cameligo.ml
index 530b46042..2725bf952 100644
--- a/src/passes/2-simplify/cameligo.ml
+++ b/src/passes/2-simplify/cameligo.ml
@@ -190,7 +190,7 @@ let rec simpl_type_expression : Raw.type_expr -> type_expression result = fun te
       let%bind cst =
         trace (unknown_predefined_type name) @@
         type_operators name.value in
-      ok @@ t_operator cst lst'
+      t_operator cst lst'
     )
   | TProd p -> (
       let%bind tpl = simpl_list_type_expression  @@ npseq_to_list p.value in
diff --git a/src/passes/2-simplify/pascaligo.ml b/src/passes/2-simplify/pascaligo.ml
index 6aea532e0..e945be8eb 100644
--- a/src/passes/2-simplify/pascaligo.ml
+++ b/src/passes/2-simplify/pascaligo.ml
@@ -250,7 +250,7 @@ let rec simpl_type_expression (t:Raw.type_expr) : type_expression result =
       let%bind cst =
         trace (unknown_predefined_type name) @@
         type_operators name.value in
-      ok @@ t_operator cst lst
+      t_operator cst lst
   | TProd p ->
       let%bind tpl = simpl_list_type_expression
     @@ npseq_to_list p.value in
diff --git a/src/stages/ast_simplified/PP.mli b/src/stages/ast_simplified/PP.mli
index 9769e2396..afa18bb0c 100644
--- a/src/stages/ast_simplified/PP.mli
+++ b/src/stages/ast_simplified/PP.mli
@@ -8,8 +8,8 @@ val list_sep_d : (formatter -> 'a -> unit) -> formatter -> 'a list -> unit
 
 val smap_sep_d : (formatter -> 'a -> unit) -> formatter -> 'a Map.String.t -> unit
 
-val type_expression : formatter -> type_expression -> unit
 *)
+val type_expression : formatter -> type_expression -> unit
 
 val literal : formatter -> literal -> unit
 
diff --git a/src/stages/ast_simplified/combinators.ml b/src/stages/ast_simplified/combinators.ml
index a13edc14f..eb00a86a6 100644
--- a/src/stages/ast_simplified/combinators.ml
+++ b/src/stages/ast_simplified/combinators.ml
@@ -12,6 +12,10 @@ module Errors = struct
       ("location" , fun () -> Format.asprintf "%a" Location.pp location) ;
     ] in
     error ~data title message
+  let bad_type_operator type_op =
+    let title () = Format.asprintf "bad type operator %a" (Stage_common.PP.type_operator PP.type_expression) type_op in
+    let message () = "" in
+    error title message
 end
 open Errors
 
@@ -57,14 +61,15 @@ let t_set key               : type_expression = make_t @@ T_operator (TC_set key
 let t_contract contract     : type_expression = make_t @@ T_operator (TC_contract contract)
 
 (* TODO find a better way than using list*)
-let t_operator op lst: type_expression =
-  match op with 
-  | TC_set _ -> t_set (List.hd lst)
-  | TC_list _ -> t_list (List.hd lst)
-  | TC_option _ -> t_option (List.hd lst)
-  | TC_map (_,_) -> let tl = List.tl lst in t_map (List.hd lst) (List.hd tl)
-  | TC_big_map (_,_) -> let tl = List.tl lst in t_big_map (List.hd lst) (List.hd tl)
-  | TC_contract _ -> t_contract (List.hd lst)
+let t_operator op lst: type_expression result =
+  match op,lst with 
+  | TC_set _         , [t] -> ok @@ t_set t
+  | TC_list _        , [t] -> ok @@ t_list t
+  | TC_option _      , [t] -> ok @@ t_option t
+  | TC_map (_,_)     , [kt;vt] -> ok @@ t_map kt vt
+  | TC_big_map (_,_) , [kt;vt] -> ok @@ t_big_map kt vt
+  | TC_contract _    , [t] -> ok @@ t_contract t
+  | _ , _ -> fail @@ bad_type_operator op
 
 let location_wrap ?(loc = Location.generated) expression =
   let location = loc in
diff --git a/src/stages/ast_simplified/combinators.mli b/src/stages/ast_simplified/combinators.mli
index a060fb865..b3a0751e0 100644
--- a/src/stages/ast_simplified/combinators.mli
+++ b/src/stages/ast_simplified/combinators.mli
@@ -42,7 +42,7 @@ val ez_t_sum : ( string * type_expression ) list -> type_expression
 val t_function : type_expression -> type_expression -> type_expression
 val t_map : type_expression -> type_expression -> type_expression
 
-val t_operator : 'a type_operator -> type_expression list -> type_expression
+val t_operator : type_expression type_operator -> type_expression list -> type_expression result
 val t_set : type_expression -> type_expression
 
 val e_var : ?loc:Location.t -> string -> expression
diff --git a/src/test/contracts/bad_type_operator.ligo b/src/test/contracts/bad_type_operator.ligo
new file mode 100644
index 000000000..eff64ad66
--- /dev/null
+++ b/src/test/contracts/bad_type_operator.ligo
@@ -0,0 +1,4 @@
+type t is (nat * nat)
+type s is map(t)      
+
+function main (const u : unit; const s : s) : (list(operation) * s) is ((nil : list(operation)), s)