diff --git a/src/PhpSpreadsheet/Shared/StringHelper.php b/src/PhpSpreadsheet/Shared/StringHelper.php
index 323aff408f..34005e6017 100644
--- a/src/PhpSpreadsheet/Shared/StringHelper.php
+++ b/src/PhpSpreadsheet/Shared/StringHelper.php
@@ -722,4 +722,19 @@ public static function convertPostToString(string $index, string $default = ''):
 
         return $default;
     }
+
+    /**
+     * Php introduced str_increment with Php8.3,
+     * but didn't issue deprecation notices till 8.5.
+     *
+     * @codeCoverageIgnore
+     */
+    public static function stringIncrement(string &$str): void
+    {
+        if (function_exists('str_increment')) {
+            $str = str_increment($str); // @phpstan-ignore-line
+        } else {
+            ++$str; // @phpstan-ignore-line
+        }
+    }
 }
diff --git a/src/PhpSpreadsheet/Writer/Html.php b/src/PhpSpreadsheet/Writer/Html.php
index 2cdbd38679..fa558f45f5 100644
--- a/src/PhpSpreadsheet/Writer/Html.php
+++ b/src/PhpSpreadsheet/Writer/Html.php
@@ -571,7 +571,7 @@ public function generateSheetData(): string
                         }
                         ++$column;
                         /** @var string $colStr */
-                        ++$colStr;
+                        StringHelper::stringIncrement($colStr);
                     }
                     $html .= $this->generateRow($sheet, $rowData, $row - 1, $cellType);
                 }
@@ -941,7 +941,7 @@ private function buildCssPerSheet(Worksheet $sheet, array &$css): void
             if ($this->shouldGenerateColumn($sheet, $colStr)) {
                 $css['table.sheet' . $sheetIndex . ' col.col' . $column]['width'] = self::DEFAULT_CELL_WIDTH_POINTS . 'pt';
             }
-            ++$colStr;
+            StringHelper::stringIncrement($colStr);
         }
 
         // col elements, loop through columnDimensions and set width
diff --git a/src/PhpSpreadsheet/Writer/Pdf/Dompdf.php b/src/PhpSpreadsheet/Writer/Pdf/Dompdf.php
index 294e020c46..0c073c521f 100644
--- a/src/PhpSpreadsheet/Writer/Pdf/Dompdf.php
+++ b/src/PhpSpreadsheet/Writer/Pdf/Dompdf.php
@@ -44,6 +44,13 @@ public function save($filename, int $flags = 0): void
         $orientation = ($orientation == 'L') ? 'landscape' : 'portrait';
 
         //  Create PDF
+        $restoreHandler = false;
+        if (PHP_VERSION_ID >= self::$temporaryVersionCheck) {
+            // @codeCoverageIgnoreStart
+            set_error_handler(self::specialErrorHandler(...));
+            $restoreHandler = true;
+            // @codeCoverageIgnoreEnd
+        }
         $pdf = $this->createExternalWriterInstance();
         $pdf->setPaper($paperSize, $orientation);
 
@@ -53,6 +60,27 @@ public function save($filename, int $flags = 0): void
         //  Write to file
         fwrite($fileHandle, $pdf->output() ?? '');
 
+        if ($restoreHandler) {
+            restore_error_handler(); // @codeCoverageIgnore
+        }
         parent::restoreStateAfterSave();
     }
+
+    protected static int $temporaryVersionCheck = 80500;
+
+    /**
+     * Temporary handler for Php8.5 waiting for Dompdf release.
+     *
+     * @codeCoverageIgnore
+     */
+    public function specialErrorHandler(int $errno, string $errstr, string $filename, int $lineno): bool
+    {
+        if ($errno === E_DEPRECATED) {
+            if (preg_match('/canonical|imagedestroy/', $errstr) === 1) {
+                return true;
+            }
+        }
+
+        return false; // continue error handling
+    }
 }
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 79adbabc4e..11e115ad6d 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -6,6 +6,9 @@
 
 function phpunit10ErrorHandler(int $errno, string $errstr, string $filename, int $lineno): bool
 {
+    if (strIncrement85(PHP_VERSION_ID, $errno, $errstr, $filename)) {
+        return true; // message suppressed - stop error handling
+    }
     $x = error_reporting() & $errno;
     if (
         in_array(
@@ -31,6 +34,21 @@ function phpunit10ErrorHandler(int $errno, string $errstr, string $filename, int
     return false; // continue error handling
 }
 
+function strIncrement85(int $version, int $errno, string $errstr, string $filename): bool
+{
+    if ($version < 80500 || $errno !== E_DEPRECATED) {
+        return false;
+    }
+    if (preg_match('/Increment on non-numeric string/', $errstr) === 1) {
+        return true;
+    }
+    if (preg_match('/canonical/', $errstr) === 1 && preg_match('/mitoteam/', $filename) === 1) {
+        return true;
+    }
+
+    return false;
+}
+
 if (!method_exists(PHPUnit\Framework\TestCase::class, 'setOutputCallback')) {
     set_error_handler('phpunit10ErrorHandler');
 }