diff --git a/src/PhpSpreadsheet/Calculation/Engineering/ConvertHex.php b/src/PhpSpreadsheet/Calculation/Engineering/ConvertHex.php
index 55ce209ecd..c0e9e458ea 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/ConvertHex.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/ConvertHex.php
@@ -96,7 +96,7 @@ public static function toDecimal($value)
         }
 
         $binX = '';
-        foreach (str_split($value) as $char) {
+        foreach (mb_str_split($value) as $char) {
             $binX .= str_pad(base_convert($char, 16, 2), 4, '0', STR_PAD_LEFT);
         }
         if (strlen($binX) == 40 && $binX[0] == '1') {
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/ConvertOctal.php b/src/PhpSpreadsheet/Calculation/Engineering/ConvertOctal.php
index add7aba01b..44af5cff4e 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/ConvertOctal.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/ConvertOctal.php
@@ -96,7 +96,7 @@ public static function toDecimal($value)
         }
 
         $binX = '';
-        foreach (str_split($value) as $char) {
+        foreach (mb_str_split($value) as $char) {
             $binX .= str_pad(decbin((int) $char), 3, '0', STR_PAD_LEFT);
         }
         if (strlen($binX) == 30 && $binX[0] == '1') {
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Arabic.php b/src/PhpSpreadsheet/Calculation/MathTrig/Arabic.php
index ee4885057f..bdc0e500e9 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Arabic.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Arabic.php
@@ -60,7 +60,7 @@ private static function mollifyScrutinizer($value): array
 
     private static function strSplit(string $roman): array
     {
-        $rslt = str_split($roman);
+        $rslt = mb_str_split($roman);
 
         return self::mollifyScrutinizer($rslt);
     }
diff --git a/src/PhpSpreadsheet/Reader/Csv/Delimiter.php b/src/PhpSpreadsheet/Reader/Csv/Delimiter.php
index 029d4a186e..02360b4262 100644
--- a/src/PhpSpreadsheet/Reader/Csv/Delimiter.php
+++ b/src/PhpSpreadsheet/Reader/Csv/Delimiter.php
@@ -60,14 +60,12 @@ protected function countPotentialDelimiters(): void
 
     protected function countDelimiterValues(string $line, array $delimiterKeys): void
     {
-        $splitString = str_split($line, 1);
-        if (is_array($splitString)) {
-            $distribution = array_count_values($splitString);
-            $countLine = array_intersect_key($distribution, $delimiterKeys);
+        $splitString = mb_str_split($line, 1);
+        $distribution = array_count_values($splitString);
+        $countLine = array_intersect_key($distribution, $delimiterKeys);
 
-            foreach (self::POTENTIAL_DELIMETERS as $delimiter) {
-                $this->counts[$delimiter][] = $countLine[$delimiter] ?? 0;
-            }
+        foreach (self::POTENTIAL_DELIMETERS as $delimiter) {
+            $this->counts[$delimiter][] = $countLine[$delimiter] ?? 0;
         }
     }
 
diff --git a/src/PhpSpreadsheet/Reader/Security/XmlScanner.php b/src/PhpSpreadsheet/Reader/Security/XmlScanner.php
index ad898ae410..56040d190a 100644
--- a/src/PhpSpreadsheet/Reader/Security/XmlScanner.php
+++ b/src/PhpSpreadsheet/Reader/Security/XmlScanner.php
@@ -145,7 +145,7 @@ public function scan($xml)
         $xml = $this->toUtf8($xml);
 
         // Don't rely purely on libxml_disable_entity_loader()
-        $pattern = '/\\0?' . implode('\\0?', /** @scrutinizer ignore-type */ str_split($this->pattern)) . '\\0?/';
+        $pattern = '/\\0?' . implode('\\0?', /** @scrutinizer ignore-type */ mb_str_split($this->pattern)) . '\\0?/';
 
         if (preg_match($pattern, $xml)) {
             throw new Reader\Exception('Detected use of ENTITY in XML, spreadsheet file load() aborted to prevent XXE/XEE attacks');
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalFormattingRuleExtension.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalFormattingRuleExtension.php
index 0cdbc36851..9cfdc94262 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalFormattingRuleExtension.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalFormattingRuleExtension.php
@@ -40,7 +40,7 @@ public function __construct(?string $id = null, string $cfRule = self::CONDITION
 
     private function generateUuid(): string
     {
-        $chars = str_split('xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx');
+        $chars = mb_str_split('xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx');
 
         foreach ($chars as $i => $char) {
             if ($char === 'x') {
diff --git a/src/PhpSpreadsheet/Style/NumberFormat/DateFormatter.php b/src/PhpSpreadsheet/Style/NumberFormat/DateFormatter.php
index ba54b53593..2901327266 100644
--- a/src/PhpSpreadsheet/Style/NumberFormat/DateFormatter.php
+++ b/src/PhpSpreadsheet/Style/NumberFormat/DateFormatter.php
@@ -177,6 +177,6 @@ private static function setLowercaseCallback(array $matches): string
 
     private static function escapeQuotesCallback(array $matches): string
     {
-        return '\\' . implode('\\', /** @scrutinizer ignore-type */ str_split($matches[1]));
+        return '\\' . implode('\\', /** @scrutinizer ignore-type */ mb_str_split($matches[1]));
     }
 }
diff --git a/tests/data/Calculation/Engineering/HEX2DEC.php b/tests/data/Calculation/Engineering/HEX2DEC.php
index 0ecdd30c1e..aaf5c2e000 100644
--- a/tests/data/Calculation/Engineering/HEX2DEC.php
+++ b/tests/data/Calculation/Engineering/HEX2DEC.php
@@ -24,4 +24,5 @@
     [-2147483648, '"ff80000000"'],
     [2147483648, '"80000000"'],
     [2147483647, '"7fffffff"'],
+    [0, '""'],
 ];
diff --git a/tests/data/Calculation/Engineering/OCT2DEC.php b/tests/data/Calculation/Engineering/OCT2DEC.php
index 8ee3a170db..b234b58a48 100644
--- a/tests/data/Calculation/Engineering/OCT2DEC.php
+++ b/tests/data/Calculation/Engineering/OCT2DEC.php
@@ -17,4 +17,5 @@
     ['#NUM!', '"37777777770"'], // too many digits
     [536870911, '"3777777777"'], // highest positive
     [-536870912, '"4000000000"'], // lowest negative
+    ['0', '""'],
 ];
diff --git a/tests/data/Calculation/MathTrig/ARABIC.php b/tests/data/Calculation/MathTrig/ARABIC.php
index e2a6f46bfd..2d1ae004b4 100644
--- a/tests/data/Calculation/MathTrig/ARABIC.php
+++ b/tests/data/Calculation/MathTrig/ARABIC.php
@@ -57,4 +57,8 @@
         '#VALUE!',
         'WRONG',
     ],
+    [
+        0,
+        '',
+    ],
 ];