diff --git a/src/aeso_ast_infer_types.erl b/src/aeso_ast_infer_types.erl
index 482bd16..5a07a9f 100644
--- a/src/aeso_ast_infer_types.erl
+++ b/src/aeso_ast_infer_types.erl
@@ -767,7 +767,9 @@ check_type(Env, Type = {fun_t, Ann, NamedArgs, Args, Ret}, Arity) ->
     {fun_t, Ann, NamedArgs1, Args1, Ret1};
 check_type(_Env, Type = {uvar, _, _}, Arity) ->
     ensure_base_type(Type, Arity),
-    Type.
+    Type;
+check_type(_Env, {args_t, Ann, Ts}, _) ->
+    type_error({new_tuple_syntax, Ann, Ts}).
 
 ensure_base_type(Type, Arity) ->
     [ type_error({wrong_type_arguments, Type, Arity, 0}) || Arity /= 0 ],
@@ -2222,6 +2224,9 @@ pp_error({contract_has_no_entrypoints, Con}) ->
                   "'function'.\n", [pp_expr("", Con), pp_loc(Con)]);
 pp_error({unbound_type, Type}) ->
     io_lib:format("Unbound type ~s (at ~s).\n", [pp_type("", Type), pp_loc(Type)]);
+pp_error({new_tuple_syntax, Ann, Ts}) ->
+    io_lib:format("Invalid type\n~s  (at ~s)\nThe syntax of tuple types changed in Sophia version 4.0. Did you mean\n~s\n",
+                  [pp_type("  ", {args_t, Ann, Ts}), pp_loc(Ann), pp_type("  ", {tuple_t, Ann, Ts})]);
 pp_error(Err) ->
     io_lib:format("Unknown error: ~p\n", [Err]).
 
diff --git a/src/aeso_parser.erl b/src/aeso_parser.erl
index b3d184f..38e6d64 100644
--- a/src/aeso_parser.erl
+++ b/src/aeso_parser.erl
@@ -150,7 +150,7 @@ type() -> ?LAZY_P(type100()).
 type100() -> type200().
 
 type200() ->
-    ?RULE(many({fun_domain(), keyword('=>')}), type300(), fun_t(_1, _2)).
+    ?RULE(many({type300(), keyword('=>')}), type300(), fun_t(_1, _2)).
 
 type300() ->
     ?RULE(sep1(type400(), tok('*')), tuple_t(get_ann(lists:nth(1, _1)), _1)).
@@ -169,16 +169,15 @@ type400() ->
 typeAtom() ->
     ?LAZY_P(choice(
     [ parens(type())
+    , args_t()
     , id(), token(con), token(qcon), token(qid), tvar()
     ])).
 
-fun_domain() -> ?LAZY_P(choice(
-    [ ?RULE(tok('('), tok(')'), [])
-      %% Note avoidance of ambiguity: `(int)` can be treated as:
-      %% - literally `int`
-      %% - list of arguments with just one element – int. This approach is dropped.
-    , ?RULE(tok('('), type(), tok(','), sep1(type(), tok(',')), tok(')'), [_2|_4])
-    , ?RULE(type300(), [_1])
+args_t() ->
+    ?LAZY_P(choice(
+    [ ?RULE(tok('('), tok(')'), {args_t, get_ann(_1), []})
+      %% Singleton case handled separately
+    , ?RULE(tok('('), type(), tok(','), sep1(type(), tok(',')), tok(')'), {args_t, get_ann(_1), [_2|_4]})
     ])).
 
 %% -- Statements -------------------------------------------------------------
@@ -501,7 +500,8 @@ tuple_t(_Ann, [Type]) -> Type;  %% Not a tuple
 tuple_t(Ann, Types)   -> {tuple_t, Ann, Types}.
 
 fun_t(Domains, Type) ->
-    lists:foldr(fun({Dom, Ann}, T) -> {fun_t, Ann, [], Dom, T} end,
+    lists:foldr(fun({{args_t, _, Dom}, Ann}, T) -> {fun_t, Ann, [], Dom, T};
+                    ({Dom, Ann}, T)             -> {fun_t, Ann, [], [Dom], T} end,
                 Type, Domains).
 
 tuple_e(_Ann, [Expr]) -> Expr;  %% Not a tuple
diff --git a/src/aeso_pretty.erl b/src/aeso_pretty.erl
index e368354..dc36374 100644
--- a/src/aeso_pretty.erl
+++ b/src/aeso_pretty.erl
@@ -243,6 +243,8 @@ type({app_t, _, Type, Args}) ->
     beside(type(Type), args_type(Args));
 type({tuple_t, _, Args}) ->
     tuple_type(Args);
+type({args_t, _, Args}) ->
+    args_type(Args);
 type({bytes_t, _, any}) -> text("bytes(_)");
 type({bytes_t, _, Len}) ->
     text(lists:concat(["bytes(", Len, ")"]));