diff --git a/src/PhpSpreadsheet/Calculation/Calculation.php b/src/PhpSpreadsheet/Calculation/Calculation.php
index 2d3a28ca..cd269be2 100644
--- a/src/PhpSpreadsheet/Calculation/Calculation.php
+++ b/src/PhpSpreadsheet/Calculation/Calculation.php
@@ -2395,10 +2395,10 @@ class Calculation
 
         if (self::$functionReplaceToLocale === null) {
             self::$functionReplaceToLocale = [];
-            foreach (array_values(self::$localeFunctions) as $localeFunctionName) {
+            foreach (self::$localeFunctions as $localeFunctionName) {
                 self::$functionReplaceToLocale[] = '$1' . trim($localeFunctionName) . '$2';
             }
-            foreach (array_values(self::$localeBoolean) as $localeBoolean) {
+            foreach (self::$localeBoolean as $localeBoolean) {
                 self::$functionReplaceToLocale[] = '$1' . trim($localeBoolean) . '$2';
             }
         }
@@ -2414,10 +2414,10 @@ class Calculation
     {
         if (self::$functionReplaceFromLocale === null) {
             self::$functionReplaceFromLocale = [];
-            foreach (array_values(self::$localeFunctions) as $localeFunctionName) {
+            foreach (self::$localeFunctions as $localeFunctionName) {
                 self::$functionReplaceFromLocale[] = '/(@?[^\w\.])' . preg_quote($localeFunctionName, '/') . '([\s]*\()/Ui';
             }
-            foreach (array_values(self::$localeBoolean) as $excelBoolean) {
+            foreach (self::$localeBoolean as $excelBoolean) {
                 self::$functionReplaceFromLocale[] = '/(@?[^\w\.])' . preg_quote($excelBoolean, '/') . '([^\w\.])/Ui';
             }
         }
diff --git a/src/PhpSpreadsheet/Calculation/Functions.php b/src/PhpSpreadsheet/Calculation/Functions.php
index bf11ceaf..b06cc4a7 100644
--- a/src/PhpSpreadsheet/Calculation/Functions.php
+++ b/src/PhpSpreadsheet/Calculation/Functions.php
@@ -355,7 +355,7 @@ class Functions
             return false;
         }
 
-        return in_array($value, array_values(self::$errorCodes));
+        return in_array($value, self::$errorCodes);
     }
 
     /**
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig.php b/src/PhpSpreadsheet/Calculation/MathTrig.php
index b6bd01cb..68aaf7b6 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig.php
@@ -1090,7 +1090,7 @@ class MathTrig
                 if ($cellReference->getWorksheet()->cellExists($column . $row)) {
                     //take this cell out if it contains the SUBTOTAL formula
                     $isFormula = $cellReference->getWorksheet()->getCell($column . $row)->isFormula();
-                    $cellFormula = !preg_match('/^=.*\bSUBTOTAL\s*\(/', strtoupper($cellReference->getWorksheet()->getCell($column . $row)->getValue()));
+                    $cellFormula = !preg_match('/^=.*\bSUBTOTAL\s*\(/i', $cellReference->getWorksheet()->getCell($column . $row)->getValue());
 
                     return !$isFormula || $cellFormula;
                 }
diff --git a/src/PhpSpreadsheet/Reader/Xml.php b/src/PhpSpreadsheet/Reader/Xml.php
index e4f866d9..65babc38 100644
--- a/src/PhpSpreadsheet/Reader/Xml.php
+++ b/src/PhpSpreadsheet/Reader/Xml.php
@@ -76,7 +76,7 @@ class Xml extends BaseReader
         // Read sample data (first 2 KB will do)
         $data = fread($fileHandle, 2048);
         fclose($fileHandle);
-        $data = strtr($data, "'", '"'); // fix headers with single quote
+        $data = str_replace("'", '"', $data); // fix headers with single quote
 
         $valid = true;
         foreach ($signature as $match) {