diff --git a/CHANGELOG.md b/CHANGELOG.md
index a08ff597..35d9d5cd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 - Fix handling for escaped enclosures and new lines in CSV Separator Inference
 - Fix MATCH an error was appearing when comparing strings against 0 (always true)
+- Fix VLOOKUP 
 - Fix return type hint
 
 ## [1.6.0] - 2019-01-02
diff --git a/src/PhpSpreadsheet/Calculation/LookupRef.php b/src/PhpSpreadsheet/Calculation/LookupRef.php
index b71313ee..e6b0f320 100644
--- a/src/PhpSpreadsheet/Calculation/LookupRef.php
+++ b/src/PhpSpreadsheet/Calculation/LookupRef.php
@@ -4,6 +4,7 @@ namespace PhpOffice\PhpSpreadsheet\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Cell\Cell;
 use PhpOffice\PhpSpreadsheet\Cell\Coordinate;
+use PhpOffice\PhpSpreadsheet\Shared\StringHelper;
 use PhpOffice\PhpSpreadsheet\Worksheet\Worksheet;
 
 class LookupRef
@@ -473,8 +474,9 @@ class LookupRef
         $lookupValue = Functions::flattenSingleValue($lookupValue);
         $matchType = ($matchType === null) ? 1 : (int) Functions::flattenSingleValue($matchType);
 
+        $initialLookupValue = $lookupValue;
         // MATCH is not case sensitive
-        $lookupValue = strtolower($lookupValue);
+        $lookupValue = StringHelper::strToLower($lookupValue);
 
         // Lookup_value type has to be number, text, or logical values
         if ((!is_numeric($lookupValue)) && (!is_string($lookupValue)) && (!is_bool($lookupValue))) {
@@ -502,7 +504,7 @@ class LookupRef
             }
             // Convert strings to lowercase for case-insensitive testing
             if (is_string($lookupArrayValue)) {
-                $lookupArray[$i] = strtolower($lookupArrayValue);
+                $lookupArray[$i] = StringHelper::strToLower($lookupArrayValue);
             }
             if (($lookupArrayValue === null) && (($matchType == 1) || ($matchType == -1))) {
                 $lookupArray = array_slice($lookupArray, 0, $i - 1);
@@ -665,7 +667,9 @@ class LookupRef
     {
         reset($a);
         $firstColumn = key($a);
-        if (($aLower = strtolower($a[$firstColumn])) == ($bLower = strtolower($b[$firstColumn]))) {
+        $aLower = StringHelper::strToLower($a[$firstColumn]);
+        $bLower = StringHelper::strToLower($b[$firstColumn]);
+        if ($aLower == $bLower) {
             return 0;
         }
 
@@ -711,11 +715,14 @@ class LookupRef
             uasort($lookup_array, ['self', 'vlookupSort']);
         }
 
+        $lookupLower = StringHelper::strToLower($lookup_value);
         $rowNumber = $rowValue = false;
         foreach ($lookup_array as $rowKey => $rowData) {
+            $firstLower = StringHelper::strToLower($rowData[$firstColumn]);
+
             // break if we have passed possible keys
             if ((is_numeric($lookup_value) && is_numeric($rowData[$firstColumn]) && ($rowData[$firstColumn] > $lookup_value)) ||
-                (!is_numeric($lookup_value) && !is_numeric($rowData[$firstColumn]) && (strtolower($rowData[$firstColumn]) > strtolower($lookup_value)))) {
+                (!is_numeric($lookup_value) && !is_numeric($rowData[$firstColumn]) && ($firstLower > $lookupLower))) {
                 break;
             }
             // remember the last key, but only if datatypes match
@@ -723,17 +730,15 @@ class LookupRef
                 (!is_numeric($lookup_value) && !is_numeric($rowData[$firstColumn]))) {
                 if ($not_exact_match) {
                     $rowNumber = $rowKey;
-                    $rowValue = $rowData[$firstColumn];
 
                     continue;
-                } elseif ((strtolower($rowData[$firstColumn]) == strtolower($lookup_value))
+                } elseif (($firstLower == $lookupLower)
                     // Spreadsheets software returns first exact match,
                     // we have sorted and we might have broken key orders
                     // we want the first one (by its initial index)
                     && (($rowNumber == false) || ($rowKey < $rowNumber))
                 ) {
                     $rowNumber = $rowKey;
-                    $rowValue = $rowData[$firstColumn];
                 }
             }
         }
@@ -786,8 +791,11 @@ class LookupRef
             // break if we have passed possible keys
             $bothNumeric = is_numeric($lookup_value) && is_numeric($rowData);
             $bothNotNumeric = !is_numeric($lookup_value) && !is_numeric($rowData);
+            $lookupLower = StringHelper::strToLower($lookup_value);
+            $rowDataLower = StringHelper::strToLower($rowData);
+
             if (($bothNumeric && $rowData > $lookup_value) ||
-                ($bothNotNumeric && strtolower($rowData) > strtolower($lookup_value))) {
+                ($bothNotNumeric && $rowDataLower > $lookupLower)) {
                 break;
             }
 
@@ -797,7 +805,7 @@ class LookupRef
                     $rowNumber = $rowKey;
 
                     continue;
-                } elseif (strtolower($rowData) === strtolower($lookup_value)
+                } elseif ($rowDataLower === $lookupLower
                     && ($rowNumber === null || $rowKey < $rowNumber)
                 ) {
                     $rowNumber = $rowKey;
diff --git a/tests/data/Calculation/LookupRef/LOOKUP.php b/tests/data/Calculation/LookupRef/LOOKUP.php
index 667d7fd1..a39f5e9a 100644
--- a/tests/data/Calculation/LookupRef/LOOKUP.php
+++ b/tests/data/Calculation/LookupRef/LOOKUP.php
@@ -106,6 +106,21 @@ return [
             ['author_100'],
             ['author_101']
         ]
+    ],
+
+    [
+        '#N/A',
+        '10y2',
+        [
+            ['5y-1'],
+            ['10y1'],
+            ['10y2'],
+        ],
+        [
+            [2.0],
+            [7.0],
+            [10.0],
+        ],
     ]
 
 ];
diff --git a/tests/data/Calculation/LookupRef/VLOOKUP.php b/tests/data/Calculation/LookupRef/VLOOKUP.php
index 1ba30a47..95c1ce5a 100644
--- a/tests/data/Calculation/LookupRef/VLOOKUP.php
+++ b/tests/data/Calculation/LookupRef/VLOOKUP.php
@@ -311,5 +311,17 @@ return [
         ],
         2,
         false
+    ],
+
+    [
+        '#N/A',
+        '10y2',
+        [
+            ['5y-1', 2.0],
+            ['10y1', 7.0],
+            ['10y2', 10.0]
+        ],
+        2.0
     ]
+
 ];