diff --git a/lib/fast_excel.rb b/lib/fast_excel.rb
index 1f6bebf..945df68 100644
--- a/lib/fast_excel.rb
+++ b/lib/fast_excel.rb
@@ -451,11 +451,11 @@ def write_value(row_number, cell_number, value, format = nil)
       if value.is_a?(Numeric)
         write_number(row_number, cell_number, value, format)
       elsif defined?(Date) && value.is_a?(Date)
-        write_datetime(row_number, cell_number, FastExcel.lxw_datetime(value.to_datetime), format)
+        write_datetime(row_number, cell_number, FastExcel.lxw_datetime(value.to_datetime.new_offset('+0000')), format)
       elsif value.is_a?(Time)
-        write_number(row_number, cell_number, FastExcel.date_num(value), format)
+        write_number(row_number, cell_number, FastExcel.date_num(value.getutc, 0), format)
       elsif defined?(DateTime) && value.is_a?(DateTime)
-        write_number(row_number, cell_number, FastExcel.date_num(value), format)
+        write_number(row_number, cell_number, FastExcel.date_num(value.new_offset('+0000'), 0), format)
       elsif value.is_a?(TrueClass) || value.is_a?(FalseClass)
         write_boolean(row_number, cell_number, value ? 1 : 0, format)
       elsif value.is_a?(FastExcel::Formula)
diff --git a/test/date_test.rb b/test/date_test.rb
index bcd46b0..84868f8 100644
--- a/test/date_test.rb
+++ b/test/date_test.rb
@@ -2,55 +2,83 @@
 
 describe "FastExcel.date_num" do
 
-  it "should save correct date" do
+  it "should correct save a Date" do
     workbook = FastExcel.open("test.xlsx", constant_memory: true)
     worksheet = workbook.add_worksheet("Payments Report")
 
     date_format = workbook.number_format("[$-409]m/d/yy h:mm AM/PM;@")
     worksheet.set_column(0, 0, 20, date_format)
 
-    date = DateTime.parse('2017-03-01 15:15:15 +0000').to_time
+    value = DateTime.parse('2017-03-01 15:15:15 +0000').to_time
 
-    worksheet.write_number(0, 0, FastExcel.date_num(date), nil)
+    worksheet.write_number(0, 0, FastExcel.date_num(value), nil)
     workbook.close
 
     data = parse_xlsx_as_matrix("test.xlsx")
 
-    assert_equal(data[0][0].to_time, date)
+    assert_equal(value, data[0][0].to_time)
   end
 
 end
 
 describe "FastExcel.write_value" do
+  # Write a value to XLSX in a specific format, then parse it and return it.
+  def convert_via_xlsx(value, number_format)
+    tmp_filename = 'test.xlsx'
+    workbook = FastExcel.open(tmp_filename, constant_memory: true)
+    worksheet = workbook.add_worksheet("Conversion test")
 
-  it "should save correct datetime" do
-    workbook = FastExcel.open(constant_memory: true)
-    worksheet = workbook.add_worksheet
-
-    format = workbook.number_format("yyyy-mm-dd hh:mm:ss")
-    value = DateTime.parse('2017-03-01 15:15:15 +0000')
-
+    format = workbook.number_format(number_format)
     worksheet.write_value(0, 0, value, format)
     workbook.close
 
-    data = parse_xlsx_as_matrix(workbook.filename)
+    data = parse_xlsx_as_matrix(tmp_filename)
 
-    assert_equal(data[0][0], value)
+    return data[0][0]
   end
 
-  it "should save correct date" do
-    workbook = FastExcel.open(constant_memory: true)
-    worksheet = workbook.add_worksheet
+  it "should correctly save a DateTime without zone offset" do
+    value = DateTime.parse('2017-03-01 15:15:15 +0000')
+    xlsx_value = convert_via_xlsx(value, "yyyy-mm-dd hh:mm:ss")
+    assert_equal(value, xlsx_value)
+  end
 
-    format = workbook.number_format("yyyy-mm-dd")
-    value = Date.parse('2017-03-01')
+  it "should correctly save and convert a DateTime with offset to +0000" do
+    value = DateTime.parse('2017-01-01 15:11:22 +0100')
+    utc_value = DateTime.parse('2017-01-01 14:11:22 +0000')
+    xlsx_value = convert_via_xlsx(value, "yyyy-mm-dd hh:mm:ss")
+    assert_equal(utc_value, xlsx_value)
+  end
 
-    worksheet.write_value(0, 0, value, format)
-    workbook.close
+  it "should correctly save and convert a DateTime with timezone to +0000" do
+    value = DateTime.parse('2017-01-01 15:11:22 CET')
+    utc_value = DateTime.parse('2017-01-01 14:11:22 +0000')
+    xlsx_value = convert_via_xlsx(value, "yyyy-mm-dd hh:mm:ss")
+    assert_equal(utc_value, xlsx_value)
+  end
 
-    data = parse_xlsx_as_matrix(workbook.filename)
+  it "should correctly save and convert a DateTime with DST timezone to +0000" do
+    value = DateTime.parse('2017-07-01 15:11:22 CEST')
+    utc_value = DateTime.parse('2017-07-01 13:11:22 +0000')
+    xlsx_value = convert_via_xlsx(value, "yyyy-mm-dd hh:mm:ss")
+    assert_equal(utc_value, xlsx_value)
+  end
 
-    assert_equal(data[0][0], value)
+  it "should correctly save a Time without zone offset" do
+    value = Time.new(2022, 1, 20, 14, 43, 10, '+00:00')
+    xlsx_value = convert_via_xlsx(value, "yyyy-mm-dd hh:mm:ss")
+    assert_equal(value.to_datetime, xlsx_value)
   end
 
+  it "should correctly save a Time with zone offset" do
+    value = Time.new(2022, 1, 20, 14, 43, 10, '+01:00')
+    xlsx_value = convert_via_xlsx(value, "yyyy-mm-dd hh:mm:ss")
+    assert_equal(value.to_datetime, xlsx_value)
+  end
+
+  it "should correctly save a Date" do
+    value = Date.parse('2017-03-01')
+    xlsx_value = convert_via_xlsx(value, "yyyy-mm-dd")
+    assert_equal(value.to_datetime, xlsx_value)
+  end
 end