diff --git a/Formatter/OutputFormatter.php b/Formatter/OutputFormatter.php
index c72728b27..d7ea7267e 100644
--- a/Formatter/OutputFormatter.php
+++ b/Formatter/OutputFormatter.php
@@ -123,6 +123,10 @@ public function formatAndWrap(?string $message, int $width): string
             return '';
         }
 
+        // For ASCII-only strings, byte positions equal character positions,
+        // so we can use native strlen/substr which is much faster than Helper::length/substr.
+        $isAscii = !preg_match('/[\x80-\xFF]/', $message);
+
         $offset = 0;
         $output = '';
         $openTagRegex = '[a-z](?:[^\\\\<>]*+ | \\\\.)*';
@@ -137,11 +141,17 @@ public function formatAndWrap(?string $message, int $width): string
                 continue;
             }
 
-            // convert byte position to character position.
-            $pos = Helper::length(substr($message, 0, $pos));
-            // add the text up to the next tag
-            $output .= $this->applyCurrentStyle(Helper::substr($message, $offset, $pos - $offset), $output, $width, $currentLineLength);
-            $offset = $pos + Helper::length($text);
+            if ($isAscii) {
+                // For ASCII, byte position = character position, no conversion needed
+                $output .= $this->applyCurrentStyle(substr($message, $offset, $pos - $offset), $output, $width, $currentLineLength);
+                $offset = $pos + \strlen($text);
+            } else {
+                // convert byte position to character position.
+                $pos = Helper::length(substr($message, 0, $pos));
+                // add the text up to the next tag
+                $output .= $this->applyCurrentStyle(Helper::substr($message, $offset, $pos - $offset), $output, $width, $currentLineLength);
+                $offset = $pos + Helper::length($text);
+            }
 
             // opening tag?
             if ($open = '/' !== $text[1]) {
@@ -162,7 +172,7 @@ public function formatAndWrap(?string $message, int $width): string
             }
         }
 
-        $output .= $this->applyCurrentStyle(Helper::substr($message, $offset), $output, $width, $currentLineLength);
+        $output .= $this->applyCurrentStyle($isAscii ? substr($message, $offset) : Helper::substr($message, $offset), $output, $width, $currentLineLength);
 
         return strtr($output, ["\0" => '\\', '\\<' => '<', '\\>' => '>']);
     }
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 950f1c096..a3dd340ba 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/11.3/phpunit.xsd"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/11.5/phpunit.xsd"
          backupGlobals="false"
          colors="true"
          bootstrap="vendor/autoload.php"
@@ -20,6 +20,11 @@
     </testsuites>
 
     <source ignoreSuppressionOfDeprecations="true">
+        <deprecationTrigger>
+            <function>trigger_deprecation</function>
+            <method>Doctrine\Deprecations\Deprecation::trigger</method>
+            <method>Doctrine\Deprecations\Deprecation::triggerIfCalledFromOutside</method>
+        </deprecationTrigger>
         <include>
             <directory>./</directory>
         </include>