diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1a60764c..d2622163 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,16 +9,17 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Added
 
-- HTML writer creates a generator meta tag - [#312](https://github.com/PHPOffice/PhpSpreadsheet/issues/312) 
+- HTML writer creates a generator meta tag - [#312](https://github.com/PHPOffice/PhpSpreadsheet/issues/312)
 - Support invalid zoom value in XLSX format - [#350](https://github.com/PHPOffice/PhpSpreadsheet/pull/350)
 - Support for `_xlfn.` prefixed functions and `ISFORMULA`, `MODE.SNGL`, `STDEV.S`, `STDEV.P` - [#390](https://github.com/PHPOffice/PhpSpreadsheet/pull/390)
 
 ### Fixed
 
-- Avoid potentially unsupported PSR-16 cache keys - [#354](https://github.com/PHPOffice/PhpSpreadsheet/issues/354) 
-- Check for MIME type to know if CSV reader can read a file - [#167](https://github.com/PHPOffice/PhpSpreadsheet/issues/167) 
-- Use proper € symbol for currency format - [#379](https://github.com/PHPOffice/PhpSpreadsheet/pull/379) 
-- Read printing area correctly when skipping some sheets - [#371](https://github.com/PHPOffice/PhpSpreadsheet/issues/371) 
+- Avoid potentially unsupported PSR-16 cache keys - [#354](https://github.com/PHPOffice/PhpSpreadsheet/issues/354)
+- Check for MIME type to know if CSV reader can read a file - [#167](https://github.com/PHPOffice/PhpSpreadsheet/issues/167)
+- Use proper € symbol for currency format - [#379](https://github.com/PHPOffice/PhpSpreadsheet/pull/379)
+- Read printing area correctly when skipping some sheets - [#371](https://github.com/PHPOffice/PhpSpreadsheet/issues/371)
+- Avoid incorrectly overwriting calculated value type - [#394](https://github.com/PHPOffice/PhpSpreadsheet/issues/394)
 
 ## [1.1.0] - 2018-01-28
 
diff --git a/src/PhpSpreadsheet/Cell/Cell.php b/src/PhpSpreadsheet/Cell/Cell.php
index 6f4e3bbf..416b4a99 100644
--- a/src/PhpSpreadsheet/Cell/Cell.php
+++ b/src/PhpSpreadsheet/Cell/Cell.php
@@ -308,7 +308,7 @@ class Cell
      *    Get old calculated value (cached)
      *    This returns the value last calculated by MS Excel or whichever spreadsheet program was used to
      *        create the original spreadsheet file.
-     *    Note that this value is not guaranteed to refelect the actual calculated value because it is
+     *    Note that this value is not guaranteed to reflect the actual calculated value because it is
      *        possible that auto-calculation was disabled in the original spreadsheet, and underlying data
      *        values used by the formula have changed since it was last calculated.
      *
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
index ad8584ab..f551c60d 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
@@ -1054,6 +1054,8 @@ class Worksheet extends WriterPart
                         $pCell->getCalculatedValue() : $cellValue;
                     if (is_string($calculatedValue)) {
                         $objWriter->writeAttribute('t', 'str');
+                    } elseif (is_bool($calculatedValue)) {
+                        $objWriter->writeAttribute('t', 'b');
                     }
 
                     break;
diff --git a/tests/PhpSpreadsheetTests/Functional/TypeAttributePreservationTest.php b/tests/PhpSpreadsheetTests/Functional/TypeAttributePreservationTest.php
new file mode 100644
index 00000000..53cc718d
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Functional/TypeAttributePreservationTest.php
@@ -0,0 +1,51 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Functional;
+
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+
+class TypeAttributePreservationTest extends AbstractFunctional
+{
+    public function providerFormulae()
+    {
+        $formats = ['Xlsx'];
+        $data = require 'data/Functional/TypeAttributePreservation/Formula.php';
+
+        $result = [];
+        foreach ($formats as $f) {
+            foreach ($data as $d) {
+                $result[] = [$f, $d];
+            }
+        }
+
+        return $result;
+    }
+
+    /**
+     * Ensure saved spreadsheets maintain the correct data type.
+     *
+     * @dataProvider providerFormulae
+     *
+     * @param string $format
+     * @param array $values
+     */
+    public function testFormulae($format, array $values)
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $sheet->fromArray($values);
+
+        $reloadedSpreadsheet = $this->writeAndReload($spreadsheet, $format);
+        $reloadedSheet = $reloadedSpreadsheet->getActiveSheet();
+
+        $expected = $sheet->getCell('A1')->getCalculatedValue();
+
+        if ($sheet->getCell('A1')->getDataType() === 'f') {
+            $actual = $reloadedSheet->getCell('A1')->getOldCalculatedValue();
+        } else {
+            $actual = $reloadedSheet->getCell('A1')->getValue();
+        }
+
+        self::assertSame($expected, $actual);
+    }
+}
diff --git a/tests/data/Functional/TypeAttributePreservation/Formula.php b/tests/data/Functional/TypeAttributePreservation/Formula.php
new file mode 100644
index 00000000..3f6b144b
--- /dev/null
+++ b/tests/data/Functional/TypeAttributePreservation/Formula.php
@@ -0,0 +1,40 @@
+<?php
+
+return [
+    [
+        ['string'],
+    ],
+    [
+        ['="string"'],
+    ],
+    [
+        [1],
+    ],
+    [
+        [0],
+    ],
+    [
+        [true],
+    ],
+    [
+        [false],
+    ],
+    [
+        ['=TRUE()'],
+    ],
+    [
+        ['=ISFORMULA(B1)', '=1+2'],
+    ],
+    [
+        ['1'],
+    ],
+    [
+        ['0'],
+    ],
+    [
+        ['null'],
+    ],
+    [
+        [null],
+    ],
+];