diff --git a/src/aeso_aci.erl b/src/aeso_aci.erl
index 5a629cd..422fb77 100644
--- a/src/aeso_aci.erl
+++ b/src/aeso_aci.erl
@@ -356,6 +356,9 @@ typedef_vars(#type_def{vars=Vars}) -> Vars.
 
 typedef_def(#type_def{typedef=Def}) -> Def.
 
+%% parse(ContractString, Options) -> {ok,AST}.
+%%  Signal errors, the sophia compiler way. Sigh!
+
 parse(Text, Options) ->
     %% Try and return something sensible here!
     case aeso_parser:string(Text, Options) of
diff --git a/test/aeso_aci_tests.erl b/test/aeso_aci_tests.erl
index fd6ab0c..8b5e1d7 100644
--- a/test/aeso_aci_tests.erl
+++ b/test/aeso_aci_tests.erl
@@ -5,17 +5,19 @@
 
 do_test() ->
     test_contract(1),
-    test_contract(2).
+    test_contract(2),
+    test_contract(3).
 
 test_contract(N) ->
-    {Contract,DecACI} = test_cases(N),
-    {ok,Enc} = aeso_aci:encode(Contract),
-    ?assertEqual(DecACI, jsx:decode(Enc, [return_maps])).
+    {Contract,MapACI,DecACI} = test_cases(N),
+    {ok,JSON} = aeso_aci:encode(Contract),
+    ?assertEqual(MapACI, jsx:decode(JSON, [return_maps])),
+    ?assertEqual(DecACI, aeso_aci:decode(JSON)).
 
 test_cases(1) ->
     Contract = <<"contract C =\n"
 		 "  function a(i : int) = i+1\n">>,
-    DecodedACI = #{<<"contract">> =>
+    MapACI = #{<<"contract">> =>
 		   #{<<"name">> => <<"C">>,
 		     <<"type_defs">> => [],
 		     <<"functions">> =>
@@ -25,13 +27,15 @@ test_cases(1) ->
 				   <<"type">> => [<<"int">>]}],
 			    <<"returns">> => <<"int">>,
 			    <<"stateful">> => false}]}},
-    {Contract,DecodedACI};
+    DecACI = <<"contract C =\n"
+	       "  function a : (int) => int\n">>,
+    {Contract,MapACI,DecACI};
 
 test_cases(2) ->
     Contract = <<"contract C =\n"
 		 "  type allan = int\n"
 		 "  function a(i : allan) = i+1\n">>,
-    DecodedACI = #{<<"contract">> =>
+    MapACI = #{<<"contract">> =>
                        #{<<"name">> => <<"C">>,
                          <<"type_defs">> =>
                              [#{<<"name">> => <<"allan">>,
@@ -44,4 +48,29 @@ test_cases(2) ->
                                 <<"name">> => <<"a">>,
                                 <<"returns">> => <<"int">>,
                                 <<"stateful">> => false}]}},
-    {Contract,DecodedACI}.
+    DecACI = <<"contract C =\n"
+	       "  function a : (int) => int\n">>,
+    {Contract,MapACI,DecACI};
+test_cases(3) ->
+    Contract = <<"contract C =\n"
+		 "  datatype bert('a) = Bin('a)\n"
+		 "  function a(i : bert(string)) = 1\n">>,
+    MapACI = #{<<"contract">> =>
+		   #{<<"functions">> =>
+			 [#{<<"arguments">> =>
+				[#{<<"name">> => <<"i">>,
+				   <<"type">> =>
+				       [#{<<"C.bert">> => [<<"string">>]}]}],
+			    <<"name">> => <<"a">>,<<"returns">> => <<"int">>,
+			    <<"stateful">> => false}],
+		     <<"name">> => <<"C">>,
+		     <<"type_defs">> =>
+			 [#{<<"name">> => <<"bert">>,
+			    <<"typedef">> =>
+				#{<<"variant">> =>
+				      [#{<<"Bin">> => [<<"'a">>]}]},
+			    <<"vars">> => [#{<<"name">> => <<"'a">>}]}]}},
+    DecACI = <<"contract C =\n"
+	       "  datatype bert('a) = Bin('a)\n"
+	       "  function a : (C.bert(string)) => int\n">>,
+    {Contract,MapACI,DecACI}.