diff --git a/src/leveled_bookie.erl b/src/leveled_bookie.erl
index b606b2f..901f6b8 100644
--- a/src/leveled_bookie.erl
+++ b/src/leveled_bookie.erl
@@ -163,6 +163,8 @@
 -type timing_types() :: head|get|put|fold.
 -type recent_aae() :: false|#recent_aae{}|undefined.
 -type key() :: binary()|string().
+    % Keys SHOULD be binary()
+    % string() support is a legacy of old tests
 -type open_options() :: 
     %% For full description of options see ../docs/STARTUP_OPTIONS.md
     [{root_path, string()|undefined} |
@@ -279,6 +281,8 @@
             % Defaults to ?COMPRESSION_POINT
         ].
 
+-export_type([key/0]).
+
 
 %%%============================================================================
 %%% API
diff --git a/src/leveled_codec.erl b/src/leveled_codec.erl
index e90f2c4..e23f04c 100644
--- a/src/leveled_codec.erl
+++ b/src/leveled_codec.erl
@@ -837,16 +837,15 @@ get_metadata_from_siblings(<<ValLen:32/integer, Rest0/binary>>,
                                     MetaBin:MetaLen/binary>>,
                                     [LastMod|LastMods]).
 
-
+-spec next_key(leveled_bookie:key()) -> leveled_bookie:key().
+%% @doc
+%% Get the next key to iterate from a given point
 next_key(Key) when is_binary(Key) ->
     <<Key/binary, 0>>;
-next_key(Key) when is_integer(Key) ->
-    Key + 1;
 next_key(Key) when is_list(Key) ->
     Key ++ [0].
 
 
-
 %%%============================================================================
 %%% Test
 %%%============================================================================