diff --git a/include/bitcask.hrl b/include/bitcask.hrl
index a62efc89..ccca2fba 100644
--- a/include/bitcask.hrl
+++ b/include/bitcask.hrl
@@ -7,13 +7,13 @@
 
 
 %% @type filestate().
--record(filestate, {mode :: 'read_only' | 'read_write',     % File mode: read_only, read_write
+-record(filestate, {mode='read_only' :: 'read_only' | 'read_write',     % File mode: read_only, read_write
                     filename :: string(), % Filename
-                    tstamp :: integer(),   % Tstamp portion of filename
-                    fd :: port(),       % File handle
-                    hintfd :: port(),   % File handle for hints
+                    tstamp=0 :: integer(),   % Tstamp portion of filename
+                    fd :: port() | undefined,       % File handle
+                    hintfd :: port() | undefined,   % File handle for hints
                     hintcrc=0 :: integer(),  % CRC-32 of current hint
-                    ofs :: non_neg_integer(), % Current offset for writing
+                    ofs=0 :: non_neg_integer(), % Current offset for writing
                     l_ofs=0 :: non_neg_integer(),  % Last offset written to data file
                     l_hbytes=0 :: non_neg_integer(),% Last # bytes written to hint file
                     l_hintcrc=0 :: non_neg_integer()}). % CRC-32 of current hint prior to last write
diff --git a/rebar.config b/rebar.config
index 045c554f..483736e1 100644
--- a/rebar.config
+++ b/rebar.config
@@ -1,4 +1,5 @@
 {erl_opts, [debug_info, warn_untyped_record,
+            {parse_transform, stacktrace_transform},
             {platform_define, "^[0-9]+", namespaced_types}]}.
 {port_specs, [{"priv/bitcask.so", ["c_src/*.c"]}]}.
 
@@ -20,6 +21,10 @@
   {"darwin10.*-32$", "LDFLAGS", "-arch i386"}
  ]}.
 
+{deps, [
+    {stacktrace_compat, "1.0.0"}
+]}.
+
 {profiles,
  [
   {prod,
diff --git a/rebar.lock b/rebar.lock
index 57afcca0..77cd0704 100644
--- a/rebar.lock
+++ b/rebar.lock
@@ -1 +1,6 @@
-[].
+{"1.1.0",
+[{<<"stacktrace_compat">>,{pkg,<<"stacktrace_compat">>,<<"1.0.0">>},0}]}.
+[
+{pkg_hash,[
+ {<<"stacktrace_compat">>, <<"78E13E0747FABC71DC725A49A4CBDDE54CEC1E9ED13BD80C1D35AC37182E1FA0">>}]}
+].
diff --git a/src/bitcask.erl b/src/bitcask.erl
index 6e5ebd25..b3a29f74 100644
--- a/src/bitcask.erl
+++ b/src/bitcask.erl
@@ -75,11 +75,11 @@
 %% @type bc_state().
 -record(bc_state, {dirname :: string(),
                    write_file :: 'fresh' | 'undefined' | #filestate{},     % File for writing
-                   write_lock :: reference(),     % Reference to write lock
-                   read_files :: [#filestate{}],     % Files opened for reading
+                   write_lock :: reference() | undefined,     % Reference to write lock
+                   read_files=[] :: [#filestate{}],     % Files opened for reading
                    max_file_size :: integer(),  % Max. size of a written file
                    opts :: list(),           % Original options used to open the bitcask
-                   key_transform :: function(),
+                   key_transform=fun kt_id/1 :: fun((binary()) -> binary()),
                    keydir :: reference(),       % Key directory
                    read_write_p :: integer(),    % integer() avoids atom -> NIF
                    % What tombstone style to write, for testing purposes only.
@@ -106,7 +106,7 @@
                   del_keydir :: reference(),
                   expiry_time :: integer(),
                   expiry_grace_time :: integer(),
-                  key_transform :: function(),
+                  key_transform=fun kt_id/1 :: fun((binary()) -> binary()),
                   read_write_p :: integer(),    % integer() avoids atom -> NIF
                   opts :: list(),
                   delete_files :: [#filestate{}]}).
@@ -635,9 +635,6 @@ merge1(Dirname, Opts, FilesToMerge0, ExpiredFiles) ->
             throw({error, not_ready})
     end,
 
-    LiveRef = make_ref(),
-    put_state(LiveRef, #bc_state{dirname = Dirname, keydir = LiveKeyDir}),
-    erlang:erase(LiveRef),
     {InFiles2,InExpiredFiles} = lists:foldl(fun(F, {InFilesAcc,InExpiredAcc}) ->
                                             case lists:member(F#filestate.filename,
                                                     ExpiredFiles) of
@@ -1378,19 +1375,13 @@ merge_files(#mstate {  dirname = Dirname,
                     } = State) ->
     FileId = bitcask_fileops:file_tstamp(File),
     F = fun(K0, V, Tstamp, Pos, State0) ->
-                K = try
-                        KT(K0)
-                    catch
-                        Err ->
-                            {key_tx_error, Err}
-                    end,
-                case K of
-                    {key_tx_error, TxErr} ->
+                try KT(K0) of
+                    K -> merge_single_entry(K, V, Tstamp, FileId, Pos, State0)
+                catch
+                    What:Why ->
                         error_logger:error_msg("Invalid key on merge ~p: ~p",
-                                               [K0, TxErr]),
-                        State0;
-                    _ ->
-                        merge_single_entry(K, V, Tstamp, FileId, Pos, State0)
+                                               [K0, {What, Why}]),
+                        State0
                 end
         end,
     State2 = try bitcask_fileops:fold(File, F, State) of
@@ -1969,14 +1960,14 @@ expiry_merge([File | Files], LiveKeyDir, KT, Acc0) ->
     Fun = fun({tombstone, _}, _, _, Acc) ->
                   Acc;
              (K0, Tstamp, {Offset, _TotalSz}, Acc) ->
-                  K = try KT(K0) catch TxErr -> {key_tx_error, TxErr} end,
-                  case K of
-                      {key_tx_error, KeyTxErr} ->
-                          error_logger:error_msg("Invalid key on merge ~p: ~p",
-                                                 [K0, KeyTxErr]);
-                      _ ->
+                  try KT(K0) of
+                      K ->
                           bitcask_nifs:keydir_remove(LiveKeyDir, K, Tstamp,
                                                      FileId, Offset)
+                  catch
+                      What:Why ->
+                          error_logger:error_msg("Invalid key on merge ~p: ~p",
+                                                 [K0, {What, Why}])
                   end,
                   Acc
         end,
@@ -1995,7 +1986,10 @@ expiry_merge([File | Files], LiveKeyDir, KT, Acc0) ->
 
 get_key_transform(KT)
   when is_function(KT) ->
-    KT;
+    case erlang:fun_info(KT, arity) of
+        {arity, 1} -> KT;
+        _ -> error(invalid_fun)
+    end;
 get_key_transform(_State) ->
     fun kt_id/1.
 
@@ -3074,6 +3068,7 @@ corrupt_file(Path, Offset, Data) ->
     ok = file:write(FH, Data),
     file:close(FH).
 
+-ifndef(OTP_RELEASE). %% only applies to OTP20 and earlier
 % Verify that if the cached efile port goes away, we can recover
 % and not get stuck opening casks
 efile_error_test() ->
@@ -3092,6 +3087,7 @@ efile_error_test() ->
         B2 when is_reference(B2) ->
             ok = bitcask:close(B2)
     end.
+-endif.
 
 %% About leak_t0():
 %%
diff --git a/src/bitcask_file.erl b/src/bitcask_file.erl
index 67a668cf..220474bb 100644
--- a/src/bitcask_file.erl
+++ b/src/bitcask_file.erl
@@ -39,8 +39,8 @@
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
          terminate/2, code_change/3]).
 
--record(state, {fd    :: file:fd(),
-                owner :: pid()}).
+-record(state, {fd    :: file:fd() | undefined,
+                owner :: pid() | undefined}).
 
 %%%===================================================================
 %%% API
diff --git a/src/bitcask_fileops.erl b/src/bitcask_fileops.erl
index aa48fb3c..a7eeb35d 100644
--- a/src/bitcask_fileops.erl
+++ b/src/bitcask_fileops.erl
@@ -783,15 +783,25 @@ hintfile_entry(Key, Tstamp, TombInt, Offset, TotalSz) ->
        TombInt:?TOMBSTONEFIELD_V2, Offset:?OFFSETFIELD_V2>>, Key].
 
 %% ===================================================================
-%% file/filelib avoidance code.
+%% file/filelib avoidance code. Only needed for pre OTP-21 releases.
 %% ===================================================================
 
+-ifdef(OTP_RELEASE).
+read_file_info(Filename) ->
+    file:read_file_info(Filename).
+
+write_file_info(FileName, Info) ->
+    file:write_file_info(FileName, Info).
+-else.
 read_file_info(FileName) ->
     prim_file:read_file_info(FileName).
 
 write_file_info(FileName, Info) ->
     prim_file:write_file_info(FileName, Info).
 
+-endif.
+
+
 is_file(File) ->
     case read_file_info(File) of
         {ok, #file_info{type=regular}} ->
@@ -840,6 +850,11 @@ ensure_dir(F) ->
 list_dir(Dir) ->
     list_dir(Dir, 1).
 
+
+-ifdef(OTP_RELEASE).
+list_dir(Directory, Retries) when is_integer(Retries), Retries > 0 ->
+    file:list_dir(Directory).
+-else.
 list_dir(_, 0) ->
     {error, efile_driver_unavailable};
 list_dir(Directory, Retries) when is_integer(Retries), Retries > 0 ->
@@ -880,4 +895,4 @@ prim_file_drv_open(Driver, Portopts) ->
         error:Reason ->
             {error, Reason}
     end.
-
+-endif.