diff --git a/src/PhpSpreadsheet/Calculation/Calculation.php b/src/PhpSpreadsheet/Calculation/Calculation.php
index f5790a1de6..1cefa64145 100644
--- a/src/PhpSpreadsheet/Calculation/Calculation.php
+++ b/src/PhpSpreadsheet/Calculation/Calculation.php
@@ -2861,7 +2861,8 @@ public function clearCalculationCacheForWorksheet($worksheetName): void
      */
     public function renameCalculationCacheForWorksheet($fromWorksheetName, $toWorksheetName): void
     {
-        if (isset($this->calculationCache[$fromWorksheetName])) {
+        // PHP 8.5: avoid using null as an array offset, coerce to empty string instead
+        if (isset($this->calculationCache[$fromWorksheetName ?? ''])) {
             $this->calculationCache[$toWorksheetName] = &$this->calculationCache[$fromWorksheetName];
             unset($this->calculationCache[$fromWorksheetName]);
         }
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/ColumnAndRowAttributes.php b/src/PhpSpreadsheet/Reader/Xlsx/ColumnAndRowAttributes.php
index 4134b2f184..db57248170 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/ColumnAndRowAttributes.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/ColumnAndRowAttributes.php
@@ -137,8 +137,9 @@ private function readColumnAttributes(SimpleXMLElement $worksheetCols, $readData
         foreach ($worksheetCols->col as $column) {
             $startColumn = Coordinate::stringFromColumnIndex((int) $column['min']);
             $endColumn = Coordinate::stringFromColumnIndex((int) $column['max']);
-            ++$endColumn;
-            for ($columnAddress = $startColumn; $columnAddress !== $endColumn; ++$columnAddress) {
+            // PHP 8.5: avoid increment on non-numeric string, use column helper instead
+            $endColumn = Coordinate::stringFromColumnIndex(Coordinate::columnIndexFromString($endColumn) + 1);
+            for ($columnAddress = $startColumn; $columnAddress !== $endColumn; $columnAddress = Coordinate::stringFromColumnIndex(Coordinate::columnIndexFromString($columnAddress) + 1)) {
                 $columnAttributes[$columnAddress] = $this->readColumnRangeAttributes($column, $readDataOnly);
 
                 if ((int) ($column['max']) == 16384) {
diff --git a/src/PhpSpreadsheet/Worksheet/Worksheet.php b/src/PhpSpreadsheet/Worksheet/Worksheet.php
index 19833b71e5..e2e43cbbea 100644
--- a/src/PhpSpreadsheet/Worksheet/Worksheet.php
+++ b/src/PhpSpreadsheet/Worksheet/Worksheet.php
@@ -2503,14 +2503,16 @@ public function rangeToArray($pRange, $nullValue = null, $calculateFormulas = tr
         $maxCol = Coordinate::stringFromColumnIndex($rangeEnd[0]);
         $maxRow = $rangeEnd[1];
 
-        ++$maxCol;
+        // PHP 8.5: avoid increment on non-numeric string, use column helper instead
+        $maxCol = Coordinate::stringFromColumnIndex(Coordinate::columnIndexFromString($maxCol) + 1);
         // Loop through rows
         $r = -1;
         for ($row = $minRow; $row <= $maxRow; ++$row) {
             $rRef = $returnCellRef ? $row : ++$r;
             $c = -1;
             // Loop through columns in the current row
-            for ($col = $minCol; $col != $maxCol; ++$col) {
+            // PHP 8.5: avoid increment on non-numeric string, use column helper instead
+            for ($col = $minCol; $col != $maxCol; $col = Coordinate::stringFromColumnIndex(Coordinate::columnIndexFromString($col) + 1)) {
                 $cRef = $returnCellRef ? $col : ++$c;
                 //    Using getCell() will create a new cell if it doesn't already exist. We don't want that to happen
                 //        so we test and retrieve directly against cellCollection