diff --git a/src/esqlite3.erl b/src/esqlite3.erl
index 90a340f..83ed700 100644
--- a/src/esqlite3.erl
+++ b/src/esqlite3.erl
@@ -269,7 +269,7 @@ get_autocommit(#esqlite3{db=Connection}) ->
 -spec exec(Connection, Sql) -> ExecResult
     when Connection :: esqlite3(),
          Sql ::  sql(),
-         ExecResult :: ok | {error, _}.
+         ExecResult :: ok | esqlite3_nif:error().
 exec(#esqlite3{db=Connection}, Sql) ->
     esqlite3_nif:exec(Connection, Sql).
 
@@ -283,7 +283,7 @@ exec(#esqlite3{db=Connection}, Sql) ->
 -spec prepare(Connection, Sql) -> PrepareResult
     when Connection :: esqlite3(),
          Sql ::  sql(),
-         PrepareResult :: {ok, esqlite3_stmt()} | {error, _}.
+         PrepareResult :: {ok, esqlite3_stmt()} | esqlite3_nif:error().
 prepare(Connection, Sql) ->
     prepare(Connection, Sql, []).
 
@@ -351,15 +351,15 @@ bind_arg(Statement, Column, {blob, Value}) ->
       Statement :: esqlite3_stmt(),
       Index :: integer(),
       Value :: integer(),
-      BindResult :: ok | {error, _}.
+      BindResult :: ok | esqlite3_nif:error().
 bind_int(#esqlite3_stmt{stmt=Stmt}, Index, Value) ->
     esqlite3_nif:bind_int(Stmt, Index, Value).
 
 -spec bind_int64(Statement, Index, Value) -> BindResult when
       Statement :: esqlite3_stmt(),
-      Index :: integer(),
+      Index :: non_neg_integer(),
       Value :: integer(),
-      BindResult :: ok | {error, _}.
+      BindResult :: ok | esqlite3_nif:error().
 bind_int64(#esqlite3_stmt{stmt=Stmt}, Index, Value) ->
     esqlite3_nif:bind_int64(Stmt, Index, Value).
 
@@ -367,7 +367,7 @@ bind_int64(#esqlite3_stmt{stmt=Stmt}, Index, Value) ->
     when Statement :: esqlite3_stmt(),
          Index :: integer(),
          Value :: float(),
-         BindResult :: ok | {error, _}.
+         BindResult :: ok | esqlite3_nif:error().
 bind_double(#esqlite3_stmt{stmt=Stmt}, Index, Value) ->
     esqlite3_nif:bind_double(Stmt, Index, Value).
 
@@ -375,7 +375,7 @@ bind_double(#esqlite3_stmt{stmt=Stmt}, Index, Value) ->
     when Statement :: esqlite3_stmt(),
          Index :: integer(),
          Value :: iodata(),
-         BindResult :: ok | {error, _}.
+         BindResult :: ok | esqlite3_nif:error().
 bind_text(#esqlite3_stmt{stmt=Stmt}, Index, Value) ->
     esqlite3_nif:bind_text(Stmt, Index, Value).
 
@@ -383,14 +383,14 @@ bind_text(#esqlite3_stmt{stmt=Stmt}, Index, Value) ->
     when Statement :: esqlite3_stmt(),
          Index :: integer(),
          Value :: iodata(),
-         BindResult :: ok | {error, _}.
+         BindResult :: ok | esqlite3_nif:error().
 bind_blob(#esqlite3_stmt{stmt=Stmt}, Index, Value) ->
     esqlite3_nif:bind_blob(Stmt, Index, Value).
 
 -spec bind_null(Statement, Index) -> BindResult
     when Statement :: esqlite3_stmt(),
          Index :: integer(),
-         BindResult :: ok | {error, _}.
+         BindResult :: ok | esqlite3_nif:error().
 bind_null(#esqlite3_stmt{stmt=Stmt}, Index) ->
     esqlite3_nif:bind_null(Stmt, Index).
 
diff --git a/src/esqlite3_nif.erl b/src/esqlite3_nif.erl
index a958254..37a314e 100644
--- a/src/esqlite3_nif.erl
+++ b/src/esqlite3_nif.erl
@@ -112,7 +112,6 @@ error_info(_Db) ->
 
 
 %% @doc Set an update hook
-%%
 -spec set_update_hook(Connection, Pid) -> Result
     when Connection :: esqlite3_ref(),
          Pid :: pid(),
@@ -122,40 +121,73 @@ set_update_hook(_Db, _Pid) ->
 
 
 %% @doc Execute a sql statement
-%%
 -spec exec(Connection, Sql) -> ExecResult 
     when Connection :: esqlite3_ref(),
          Sql :: sql(),
-         ExecResult :: ok | {error, _}.
+         ExecResult :: ok | error().
 exec(_Connection, _Sql) ->
     erlang:nif_error(nif_library_not_loaded).
 
 
 %% @doc Compile a sql statement. 
-%%
 -spec prepare(Connection, Sql, PrepareFlags) -> PrepareResult
     when Connection :: esqlite3_ref(),
          Sql :: sql(),
          PrepareFlags :: non_neg_integer(),
-         PrepareResult :: {ok, esqlite3_stmt_ref()} | {error, _}.
+         PrepareResult :: {ok, esqlite3_stmt_ref()} | error().
 prepare(_Connection, _Sql, _PrepareFlags) ->
     erlang:nif_error(nif_library_not_loaded).
 
+% @doc Bind an integer to a position in a prepared statement.
+-spec bind_int(Statement, Index, Value) -> Result when
+      Statement :: esqlite3_stmt_ref(),
+      Index :: integer(),
+      Value :: integer(), %% [todo] Should be a 32 bit integer range.
+      Result :: ok | error().
 bind_int(_Statement, _Index, _Value) ->
     erlang:nif_error(nif_library_not_loaded).
 
+% @doc Bind a 64 bit integer to a position in a prepared statement.
+-spec bind_int64(Statement, Index, Value) -> Result when
+      Statement :: esqlite3_stmt_ref(),
+      Index :: integer(),
+      Value :: integer(), %% [todo] Should be a 64 bit integer range.
+      Result :: ok | error().
 bind_int64(_Statement, _Index, _Value) ->
     erlang:nif_error(nif_library_not_loaded).
 
+% @doc Bind an double/float to a position in a prepared statement.
+-spec bind_double(Statement, Index, Value) -> Result when
+      Statement :: esqlite3_stmt_ref(),
+      Index :: integer(),
+      Value :: float(), %% [todo] Should be a 64 bit integer range.
+      Result :: ok | error().
 bind_double(_Statement, _Index, _Value) ->
     erlang:nif_error(nif_library_not_loaded).
 
+% @doc Bind a utf-8 string to a position in a prepared statement.
+-spec bind_text(Statement, Index, Value) -> Result when
+      Statement :: esqlite3_stmt_ref(),
+      Index :: integer(),
+      Value :: iodata(), %% [todo] Should be a utf-8 iodata.
+      Result :: ok | error().
 bind_text(_Statement, _Index, _Value) ->
     erlang:nif_error(nif_library_not_loaded).
 
+% @doc Bind a blob to a position in a prepared statement.
+-spec bind_blob(Statement, Index, Value) -> Result when
+      Statement :: esqlite3_stmt_ref(),
+      Index :: integer(),
+      Value :: iodata(),
+      Result :: ok | error().
 bind_blob(_Statement, _Index, _Value) ->
     erlang:nif_error(nif_library_not_loaded).
 
+% @doc Bind a null to a position in a prepared statement.
+-spec bind_null(Statement, Index) -> Result when
+      Statement :: esqlite3_stmt_ref(),
+      Index :: integer(),
+      Result :: ok | error().
 bind_null(_Statement, _Index) ->
     erlang:nif_error(nif_library_not_loaded).
 
@@ -189,7 +221,6 @@ column_decltypes(_Stmt) ->
 backup_init(_Dest, _DestName, _Src, _SrcName) ->
     erlang:nif_error(nif_library_not_loaded).
 
-
 backup_remaining(_Backup) ->
     erlang:nif_error(nif_library_not_loaded).
 
@@ -249,7 +280,7 @@ memory_stats(_Flag) ->
 -spec status(Op, HighwaterResetFlag) -> Stats when 
       Op :: integer(),
       HighwaterResetFlag :: integer(),
-      Stats :: #{ used := integer(), highwater := integer() }.
+      Stats :: #{ used := non_neg_integer(), highwater := non_neg_integer() }.
 status(_Op, _Flag) ->
     erlang:nif_error(nif_library_not_loaded).