diff --git a/CHANGES b/CHANGES
index d76407d..ae022ba 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,6 +1,18 @@
 Changelog of cowdb
 ------------------
 
+0.4.2 - 2014/01/04
+
+- Internally uses the CBT library for all of our btree usages.
+- fix: handle duplicate keys in transactions (#4)
+
+0.4.1 - 2014/08/17
+
+- New license. CowDB is now released under the Mozilla Public License v2.0
+- cowdb now uses the C4.1 (Collective Code Construction Contract) process for
+contributions.
+- move code from bitbucket to github.
+
 0.4.0 - 2014/06/30
 
 - rename cowdb:db_info/1 to cowdb:database_info/1
diff --git a/src/cowdb_updater.erl b/src/cowdb_updater.erl
index 7b5bf22..07fd4f8 100644
--- a/src/cowdb_updater.erl
+++ b/src/cowdb_updater.erl
@@ -380,12 +380,21 @@ run_transaction([{add, Key, Value} | Rest], {ToAdd, ToRem}, Log, TransactId,
     %% only keep a reference so we don't have the value multiple time.
     {ok, Pos, Size} = cbt_file:append_term_crc32(Fd, Value),
     Value1 =  {Key, {Pos, Size}, TransactId, Ts},
-    run_transaction(Rest, {[{Key, Value1} | ToAdd], ToRem},
+    %% make sure to replace duplicates
+    ToAdd2 = lists:keystore(Key, 1, ToAdd, {Key, Value1}),
+    run_transaction(Rest, {ToAdd2, ToRem},
                     [{add, Value1} | Log],  TransactId, Ts, Db);
-run_transaction([{remove, Key} | Rest], {ToAdd, ToRem}, Log, TransactId, Ts, Db) ->
-    %% remove a key
-    run_transaction(Rest, {ToAdd, [Key | ToRem]}, [{remove, Key} | Log],
-                    TransactId, Ts, Db);
+run_transaction([{remove, Key} | Rest], {ToAdd, ToRem}, Log, TransactId, Ts,
+                Db) ->
+    case lists:member(Key, ToRem) of
+        true ->
+            %% duplicate, continue
+            run_transaction(Rest, {ToAdd, ToRem}, Log, TransactId, Ts, Db);
+        false ->
+            %% remove a key
+            run_transaction(Rest, {ToAdd, [Key | ToRem]}, [{remove, Key} | Log],
+                            TransactId, Ts, Db)
+    end;
 run_transaction([{fn, Func} | Rest], AddRemove, Log, TransactId, Ts, Db) ->
     %% execute a transaction function
     case cowdb_util:apply(Func, [Db]) of
diff --git a/test/cowdb_basic_tests.erl b/test/cowdb_basic_tests.erl
index d2df68a..e080aad 100644
--- a/test/cowdb_basic_tests.erl
+++ b/test/cowdb_basic_tests.erl
@@ -64,7 +64,9 @@ basic_ops_test_() ->
                 fun should_fold_range/1,
                 fun should_cancel_transact_fun/1,
                 fun should_error_transact_fun/1,
-                fun shoudl_catch_transact_fun_error/1
+                fun shoudl_catch_transact_fun_error/1,
+                fun should_handle_duplicate_kvs/1,
+                fun should_handle_delete_with_duplicate_keys/1
         ])
     }.
 
@@ -250,3 +252,18 @@ shoudl_catch_transact_fun_error(Db) ->
     end,
     Reply = cowdb:transact(Db,  [{fn, TransactFun}]),
     ?_assertMatch(badarg, Reply).
+
+
+should_handle_duplicate_kvs(Db) ->
+    {ok, Tx} = cowdb:transact(Db, [{add, a, 1},
+                                   {add, a, 3}]),
+    ?assertEqual(1, Tx),
+    ?_assertMatch([{ok, {a, 3}}], cowdb:mget(Db, [a])).
+
+should_handle_delete_with_duplicate_keys(Db) ->
+    {ok, 1} = cowdb:mput(Db,  [{a, 1}, {b, 2}, {c, 3}]),
+    ?assertMatch([{ok, {a, 1}}, {ok, {b, 2}}, {ok, {c, 3}}],
+                  cowdb:mget(Db, [a, b, c])),
+    {ok, 2} = cowdb:mdelete(Db, [a, a, b, c]),
+    ?_assertMatch([not_found, not_found, not_found],
+                  cowdb:mget(Db, [a, b, c])).