diff --git a/src/aeb_fate_code.erl b/src/aeb_fate_code.erl
index e0b1747..1c6b5a3 100644
--- a/src/aeb_fate_code.erl
+++ b/src/aeb_fate_code.erl
@@ -302,6 +302,9 @@ deserialize_functions(<<?FUNCTION:8, A, B, C, D, Rest/binary>>,
                                          Program#{ BB => lists:reverse(Code)}}}},
             deserialize_functions(Rest2, Env2)
     end;
+deserialize_functions(<<Op:8, Rest/binary>>,
+            #{ function := none }) ->
+    error({code_without_function});
 deserialize_functions(<<Op:8, Rest/binary>>,
             #{ bb := BB
              , current_bb_code := Code
@@ -343,6 +346,7 @@ deserialize_op(Op, Rest, Code) ->
 
 deserialize_n_args(N, <<M3:2, M2:2, M1:2, M0:2, Rest/binary>>) when N =< 4 ->
     ArgMods = lists:sublist([M0, M1, M2, M3], N),
+    %% If N == 1 then we take M0 and don't care about the others. Should we check that the others are 0??
     lists:mapfoldl(fun(M, Acc) ->
                            case bits_to_modifier(M) of
                                stack ->
diff --git a/src/aeb_fate_encoding.erl b/src/aeb_fate_encoding.erl
index 59f7bbc..582839e 100644
--- a/src/aeb_fate_encoding.erl
+++ b/src/aeb_fate_encoding.erl
@@ -269,12 +269,18 @@ deserialize_types(N, Binary, Acc) ->
 rlp_encode_int(S) when S >= 0 ->
     aeser_rlp:encode(binary:encode_unsigned(S)).
 
+
+%% first byte of the binary gives the number of bytes we need <<129>> is 1, <<130>> = 2,
+%% so <<129, 0>> is <<0>> and <<130, 0, 0>> is <<0, 0>>
 rlp_decode_int(Binary) ->
-    case aeser_rlp:decode_one(Binary) of
-        {<<>>, _} ->
-            error({illegal_integer_encoding, Binary});
-        {Bin1, Rest} ->
-            {binary:decode_unsigned(Bin1), Rest}
+    {Bin1, Rest} = aeser_rlp:decode_one(Binary),
+    Int = binary:decode_unsigned(Bin1),
+    ReEncode = rlp_encode_int(Int),
+    case <<ReEncode/binary, Rest/binary>> == Binary of
+        true ->
+            {Int, Rest};
+        false ->
+            error({none_unique_encoding, Bin1, ReEncode})
     end.
 
 serialize_integer(I) when ?IS_FATE_INTEGER(I) ->