diff --git a/src/ncalendar_util.erl b/src/ncalendar_util.erl
index 1abd26b..19da4a8 100644
--- a/src/ncalendar_util.erl
+++ b/src/ncalendar_util.erl
@@ -67,14 +67,14 @@ datetimezone_to_datetime({Datetime, _Subseconds, Timezone}) ->
 -spec datetimezone_to_gregorian_seconds(Datetimezone) -> Result when
     Datetimezone :: ncalendar_format:datetimezone(),
     Result :: ncalendar:gregorian_seconds().
-datetimezone_to_gregorian_seconds({Datetime, _Subseconds, Timezone}) ->
-    calendar:datetime_to_gregorian_seconds(Datetime) + timezone_diff(Timezone).
+datetimezone_to_gregorian_seconds({Datetime, _Subseconds, _Timezone}) ->
+    calendar:datetime_to_gregorian_seconds(Datetime).
 
 -spec datetimezone_to_timestamp(Datetimezone) -> Result when
     Datetimezone :: ncalendar_format:datetimezone(),
     Result :: erlang:timestamp().
-datetimezone_to_timestamp({Datetime, {millisecond, Milliseconds}, Timezone}) ->
-    GregorianSeconds = calendar:datetime_to_gregorian_seconds(Datetime) + timezone_diff(Timezone),
+datetimezone_to_timestamp({Datetime, {millisecond, Milliseconds}, _Timezone}) ->
+    GregorianSeconds = calendar:datetime_to_gregorian_seconds(Datetime),
     Secs = GregorianSeconds - ?JANUARY_1ST_1970,
     MicroSecs = Milliseconds * 1000,
     {Secs div 1000000, Secs rem 1000000, MicroSecs}.
diff --git a/test/ncalendar_SUITE.erl b/test/ncalendar_SUITE.erl
index f221339..6d4560a 100644
--- a/test/ncalendar_SUITE.erl
+++ b/test/ncalendar_SUITE.erl
@@ -13,6 +13,9 @@
 %% limitations under the License.
 -module(ncalendar_SUITE).
 
+%%% INCLUDE FILES
+-include_lib("stdlib/include/assert.hrl").
+
 %%% EXTERNAL EXPORTS
 -compile([export_all, nowarn_export_all]).
 
@@ -162,13 +165,25 @@ convert_without_tz(_Conf) ->
 datetime(_Conf) ->
     Datetime = calendar:universal_time(),
     Bin = ncalendar:from_datetime(iso8601, Datetime),
-    Datetime = ncalendar:to_datetime(iso8601, Bin).
+    Datetime = ncalendar:to_datetime(iso8601, Bin),
+
+    ISO8601UTC = <<"20140519T100000Z">>,
+    ISO8601 = <<"20140519T100000+1000">>,
+    UTC = ncalendar:to_datetime(iso8601, ISO8601UTC),
+    Zone = ncalendar:to_datetime(iso8601, ISO8601),
+    ?assertEqual(UTC, Zone).
 
 gregorian_seconds(_Conf) ->
     Datetime = calendar:universal_time(),
     GregorianSeconds = calendar:datetime_to_gregorian_seconds(Datetime),
     Bin = ncalendar:from_gregorian_seconds(iso8601, GregorianSeconds),
-    GregorianSeconds = ncalendar:to_gregorian_seconds(iso8601, Bin).
+    GregorianSeconds = ncalendar:to_gregorian_seconds(iso8601, Bin),
+
+    ISO8601UTC = <<"20140519T100000Z">>,
+    ISO8601 = <<"20140519T100000+1000">>,
+    UTC = ncalendar:to_gregorian_seconds(iso8601, ISO8601UTC),
+    Zone = ncalendar:to_gregorian_seconds(iso8601, ISO8601),
+    ?assertNotEqual(UTC, Zone).
 
 now(_Conf) ->
     DateTime = calendar:now_to_datetime(erlang:timestamp()),
@@ -181,7 +196,13 @@ timestamp(_Conf) ->
     Timestamp = erlang:timestamp(),
     Bin = ncalendar:from_timestamp(iso8601, Timestamp),
     {MSecs, Secs, _MicroSecs1} = Timestamp,
-    {MSecs, Secs, 0} = ncalendar:to_timestamp(iso8601, Bin).
+    {MSecs, Secs, 0} = ncalendar:to_timestamp(iso8601, Bin),
+
+    ISO8601UTC = <<"20140519T100000Z">>,
+    ISO8601 = <<"20140519T100000+1000">>,
+    UTC = ncalendar:to_timestamp(iso8601, ISO8601UTC),
+    Zone = ncalendar:to_timestamp(iso8601, ISO8601),
+    ?assertNotEqual(UTC, Zone).
 
 shift_timezone(_Conf) ->
     ISO8601 = <<"20140519T100000+1000">>,