diff --git a/src/hz.erl b/src/hz.erl
index e0ba057..b76f734 100644
--- a/src/hz.erl
+++ b/src/hz.erl
@@ -78,7 +78,7 @@
 
 %%% Types
 
--export_type([chain_node/0, network_id/0, chain_error/0]).
+-export_type([chain_node/0, network_id/0, chain_error/0, aaci/0]).
 
 -include_lib("eunit/include/eunit.hrl").
 
@@ -94,6 +94,7 @@
                              | {headers, map()}
                              | bad_length
                              | gc_out_of_range.
+-type aaci()                :: {aaci, term(), term(), term()}.
 -type pubkey()              :: unicode:chardata().  % "ak_" ++ _
 -type account_id()          :: pubkey().
 -type contract_id()         :: unicode:chardata().  % "ct_" ++ _
@@ -218,8 +219,10 @@
 
 %%% Get/Set admin functions
 
--spec network_id() -> NetworkID
-    when NetworkID :: string() | none.
+-spec network_id() -> Result
+    when Result    :: {ok, NetworkID} | {error, Reason},
+         NetworkID :: string(),
+         Reason    :: term().
 %% @doc
 %% Returns the network ID or the atom `none' if it is unset.
 %% Checking this is not normally necessary, but if network ID assignment is dynamic
@@ -1150,7 +1153,7 @@ read_aci(Path) ->
 
 -spec contract_call(CallerID, AACI, ConID, Fun, Args) -> Result
     when CallerID :: unicode:chardata(),
-         AACI     :: map(),
+         AACI     :: aaci(),
          ConID    :: unicode:chardata(),
          Fun      :: string(),
          Args     :: [string()],
@@ -1185,7 +1188,7 @@ contract_call(CallerID, AACI, ConID, Fun, Args) ->
 -spec contract_call(CallerID, Gas, AACI, ConID, Fun, Args) -> Result
     when CallerID :: unicode:chardata(),
          Gas      :: pos_integer(),
-         AACI     :: map(),
+         AACI     :: aaci(),
          ConID    :: unicode:chardata(),
          Fun      :: string(),
          Args     :: [string()],
@@ -1223,7 +1226,7 @@ contract_call(CallerID, Gas, AACI, ConID, Fun, Args) ->
          GasPrice :: pos_integer(),
          Amount   :: non_neg_integer(),
          TTL      :: pos_integer(),
-         AACI     :: map(),
+         AACI     :: aaci(),
          ConID    :: unicode:chardata(),
          Fun      :: string(),
          Args     :: [string()],
@@ -1390,7 +1393,7 @@ contract_call4(PK, Nonce, Gas, GasPrice, Amount, TTL, CK, CallData) ->
 
 -spec prepare_contract(File) -> {ok, AACI} | {error, Reason}
     when File   :: file:filename(),
-         AACI   :: map(),
+         AACI   :: aaci(),
          Reason :: term().
 %% @doc
 %% Compile a contract and extract the function spec meta for use in future formation
@@ -2052,7 +2055,7 @@ zip_record_field({Name, Type}, {Remaining, Missing}) ->
     end.
 
 -spec aaci_lookup_spec(AACI, Fun) -> {ok, Type} | {error, Reason}
-    when AACI   :: {aaci, term(), term(), term()}, % FIXME
+    when AACI   :: aaci(),
          Fun    :: binary() | string(),
          Type   :: {term(), term()}, % FIXME
          Reason :: bad_fun_name.
@@ -2213,8 +2216,6 @@ spend2(DSenderID,
     end.
 
 
-decode_account_id(S) when is_list(S) ->
-    decode_account_id(list_to_binary(S));
 decode_account_id(B) ->
     try
         {account_pubkey, PK}  = gmser_api_encoder:decode(B),
@@ -2310,8 +2311,8 @@ verify_signature2(Sig, Message, PK) ->
 
 % This is Bitcoin's variable-length unsigned integer encoding
 % See: https://en.bitcoin.it/wiki/Protocol_documentation#Variable_length_integer
-vencode(N) when N < 0 ->
-    {error, {negative_N, N}};
+vencode(N) when N =< 0 ->
+    {error, {non_pos_N, N}};
 vencode(N) when N < 16#FD ->
     {ok, <<N>>};
 vencode(N) when N =< 16#FFFF ->