diff --git a/src/PhpSpreadsheet/Reader/Xlsx/ConditionalStyles.php b/src/PhpSpreadsheet/Reader/Xlsx/ConditionalStyles.php
index 8731d642e5..a03fa71b24 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/ConditionalStyles.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/ConditionalStyles.php
@@ -125,6 +125,7 @@ private function readConditionalRuleFromExt(SimpleXMLElement $cfRuleXml, SimpleX
     {
         $conditionType = (string) $attributes->type;
         $operatorType = (string) $attributes->operator;
+        $priority = (int) (string) $attributes->priority;
 
         $operands = [];
         foreach ($cfRuleXml->children($this->ns['xm']) as $cfRuleOperandsXml) {
@@ -134,6 +135,7 @@ private function readConditionalRuleFromExt(SimpleXMLElement $cfRuleXml, SimpleX
         $conditional = new Conditional();
         $conditional->setConditionType($conditionType);
         $conditional->setOperatorType($operatorType);
+        $conditional->setPriority($priority);
         if (
             $conditionType === Conditional::CONDITION_CONTAINSTEXT
             || $conditionType === Conditional::CONDITION_NOTCONTAINSTEXT
@@ -184,7 +186,7 @@ private function readConditionalStyles(SimpleXMLElement $xmlSheet): array
     private function setConditionalStyles(Worksheet $worksheet, array $conditionals, SimpleXMLElement $xmlExtLst): void
     {
         foreach ($conditionals as $cellRangeReference => $cfRules) {
-            ksort($cfRules);
+            ksort($cfRules); // no longer needed for Xlsx, but helps Xls
             $conditionalStyles = $this->readStyleRules($cfRules, $xmlExtLst);
 
             // Extract all cell references in $cellRangeReference
@@ -205,6 +207,7 @@ private function readStyleRules(array $cfRules, SimpleXMLElement $extLst): array
             $objConditional = new Conditional();
             $objConditional->setConditionType((string) $cfRule['type']);
             $objConditional->setOperatorType((string) $cfRule['operator']);
+            $objConditional->setPriority((int) (string) $cfRule['priority']);
             $objConditional->setNoFormatSet(!isset($cfRule['dxfId']));
 
             if ((string) $cfRule['text'] != '') {
diff --git a/src/PhpSpreadsheet/Style/Conditional.php b/src/PhpSpreadsheet/Style/Conditional.php
index 01a4d8a9f3..d476bdffd2 100644
--- a/src/PhpSpreadsheet/Style/Conditional.php
+++ b/src/PhpSpreadsheet/Style/Conditional.php
@@ -106,6 +106,8 @@ class Conditional implements IComparable
 
     private bool $noFormatSet = false;
 
+    private int $priority = 0;
+
     /**
      * Create a new Conditional.
      */
@@ -115,6 +117,18 @@ public function __construct()
         $this->style = new Style(false, true);
     }
 
+    public function getPriority(): int
+    {
+        return $this->priority;
+    }
+
+    public function setPriority(int $priority): self
+    {
+        $this->priority = $priority;
+
+        return $this;
+    }
+
     public function getNoFormatSet(): bool
     {
         return $this->noFormatSet;
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
index 28af258297..98ee0bd31e 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
@@ -861,7 +861,12 @@ private static function writeColorScaleElements(XMLWriter $objWriter, ?Condition
     private function writeConditionalFormatting(XMLWriter $objWriter, PhpspreadsheetWorksheet $worksheet): void
     {
         // Conditional id
-        $id = 1;
+        $id = 0;
+        foreach ($worksheet->getConditionalStylesCollection() as $conditionalStyles) {
+            foreach ($conditionalStyles as $conditional) {
+                $id = max($id, $conditional->getPriority());
+            }
+        }
 
         // Loop through styles in the current worksheet
         foreach ($worksheet->getConditionalStylesCollection() as $cellCoordinate => $conditionalStyles) {
@@ -888,7 +893,8 @@ private function writeConditionalFormatting(XMLWriter $objWriter, Phpspreadsheet
                     'dxfId',
                     (string) $this->getParentWriter()->getStylesConditionalHashTable()->getIndexForHashCode($conditional->getHashCode())
                 );
-                $objWriter->writeAttribute('priority', (string) $id++);
+                $priority = $conditional->getPriority() ?: ++$id;
+                $objWriter->writeAttribute('priority', (string) $priority);
 
                 self::writeAttributeif(
                     $objWriter,
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalPriorityTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalPriorityTest.php
new file mode 100644
index 0000000000..542b78d865
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalPriorityTest.php
@@ -0,0 +1,129 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
+
+use PhpOffice\PhpSpreadsheet\IOFactory;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Style\Conditional;
+use PhpOffice\PhpSpreadsheet\Style\Fill;
+use PhpOffice\PhpSpreadsheetTests\Functional\AbstractFunctional;
+
+class ConditionalPriorityTest extends AbstractFunctional
+{
+    public function testConditionalPriority(): void
+    {
+        $filename = 'tests/data/Reader/XLSX/issue.4312c.xlsx';
+        $reader = IOFactory::createReader('Xlsx');
+        $spreadsheet = $reader->load($filename);
+        $reloadedSpreadsheet = $this->writeAndReload($spreadsheet, 'Xlsx');
+        $spreadsheet->disconnectWorksheets();
+        $worksheet = $reloadedSpreadsheet->getActiveSheet();
+        $priorities = [];
+        foreach ($worksheet->getConditionalStylesCollection() as $conditionalStyles) {
+            foreach ($conditionalStyles as $conditional) {
+                $priorities[] = $conditional->getPriority();
+            }
+        }
+        $expected = [27, 2, 3, 4, 1, 22, 14, 5, 6, 7, 20];
+        self::assertSame($expected, $priorities);
+        $reloadedSpreadsheet->disconnectWorksheets();
+    }
+
+    public function testZeroPriority(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $sheet->fromArray([
+            [1, 1, 1, 1],
+            [2, 2, 2, 2],
+            [3, 3, 3, 3],
+            [4, 4, 4, 4],
+            [5, 5, 5, 5],
+        ]);
+
+        $range = 'A1:A5';
+        $styles = [];
+        $new = new Conditional();
+        $new->setConditionType(Conditional::CONDITION_CELLIS)
+            ->setOperatorType(Conditional::OPERATOR_EQUAL)
+            ->setPriority(30)
+            ->setConditions(['3'])
+            ->getStyle()
+            ->getFill()
+            ->setFillType(Fill::FILL_SOLID)
+            ->getStartColor()
+            ->setArgb('FFC00000');
+        $styles[] = $new;
+        $sheet->setConditionalStyles($range, $styles);
+
+        $range = 'B1:B5';
+        $styles = [];
+        $new = new Conditional();
+        $new->setConditionType(Conditional::CONDITION_EXPRESSION)
+            ->setConditions('=MOD(A1,2)=0')
+            ->getStyle()
+            ->getFill()
+            ->setFillType(Fill::FILL_SOLID)
+            ->getStartColor()
+            ->setArgb('FF00B0F0');
+        $styles[] = $new;
+        $new = new Conditional();
+        $new->setConditionType(Conditional::CONDITION_CELLIS)
+            ->setOperatorType(Conditional::OPERATOR_EQUAL)
+            ->setPriority(40)
+            ->setConditions(['4'])
+            ->getStyle()
+            ->getFill()
+            ->setFillType(Fill::FILL_SOLID)
+            ->getStartColor()
+            ->setArgb('FFFFC000');
+        $styles[] = $new;
+        $sheet->setConditionalStyles($range, $styles);
+
+        $range = 'C1:C5';
+        $styles = [];
+        $new = new Conditional();
+        $new->setConditionType(Conditional::CONDITION_CELLIS)
+            ->setOperatorType(Conditional::OPERATOR_EQUAL)
+            ->setPriority(20)
+            ->setConditions(['2'])
+            ->getStyle()
+            ->getFill()
+            ->setFillType(Fill::FILL_SOLID)
+            ->getStartColor()
+            ->setArgb('FFFFFF00');
+        $styles[] = $new;
+        $new = new Conditional();
+        $new->setConditionType(Conditional::CONDITION_CELLIS)
+            ->setOperatorType(Conditional::OPERATOR_EQUAL)
+            ->setConditions(['5'])
+            ->getStyle()
+            ->getFill()
+            ->setFillType(Fill::FILL_SOLID)
+            ->getStartColor()
+            ->setArgb('FF008080');
+        $styles[] = $new;
+        $sheet->setConditionalStyles($range, $styles);
+
+        $reloadedSpreadsheet = $this->writeAndReload($spreadsheet, 'Xlsx');
+        $spreadsheet->disconnectWorksheets();
+        $worksheet = $reloadedSpreadsheet->getActiveSheet();
+        $priorities = [];
+        foreach ($worksheet->getConditionalStylesCollection() as $conditionalStyles) {
+            foreach ($conditionalStyles as $conditional) {
+                $priorities[] = $conditional->getPriority();
+            }
+        }
+        // B1:B5 is written in order 41, 40, but Reader sorts them
+        $expected = [30, 40, 41, 20, 42];
+        self::assertSame($expected, $priorities);
+        $styles = $worksheet->getConditionalStyles('B1:B5');
+        self::assertSame(Conditional::CONDITION_CELLIS, $styles[0]->getConditionType());
+        self::assertSame(40, $styles[0]->getPriority());
+        self::assertSame(Conditional::CONDITION_EXPRESSION, $styles[1]->getConditionType());
+        self::assertSame(41, $styles[1]->getPriority());
+        $reloadedSpreadsheet->disconnectWorksheets();
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue4248Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue4248Test.php
index 06b0b7f31c..de5ec8f029 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue4248Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue4248Test.php
@@ -66,13 +66,13 @@ public function testStyles(): void
         $file .= '#xl/worksheets/sheet1.xml';
         $data = file_get_contents($file) ?: '';
         $expected = '<conditionalFormatting sqref="C16:C38 E17:H18 I17:J37 D18 J23:J38 E38 I38">'
-            . '<cfRule type="containsText" dxfId="0" priority="1" operator="containsText" text="Oui">'
+            . '<cfRule type="containsText" dxfId="0" priority="15" operator="containsText" text="Oui">'
             . '<formula>NOT(ISERROR(SEARCH(&quot;Oui&quot;,C16)))</formula>'
             . '</cfRule>'
             . '</conditionalFormatting>';
         self::assertStringContainsString($expected, $data, 'first condition for D18');
         $expected = '<conditionalFormatting sqref="C16:C38 I17:J37 E17:H18 D18 J23:J38 E38 I38">'
-            . '<cfRule type="containsText" dxfId="1" priority="2" operator="containsText" text="Non">'
+            . '<cfRule type="containsText" dxfId="1" priority="14" operator="containsText" text="Non">'
             . '<formula>NOT(ISERROR(SEARCH(&quot;Non&quot;,C16)))</formula>'
             . '</cfRule>'
             . '</conditionalFormatting>';
diff --git a/tests/data/Reader/XLSX/issue.4312c.xlsx b/tests/data/Reader/XLSX/issue.4312c.xlsx
new file mode 100644
index 0000000000..0446ed6cc0
Binary files /dev/null and b/tests/data/Reader/XLSX/issue.4312c.xlsx differ