diff --git a/ecs.php b/ecs.php
index b7b4732..29d907f 100644
--- a/ecs.php
+++ b/ecs.php
@@ -46,6 +46,7 @@
 use PhpCsFixer\Fixer\AttributeNotation\AttributeEmptyParenthesesFixer;
 use PhpCsFixer\Fixer\Basic\BracesFixer;
 use PhpCsFixer\Fixer\Basic\NoTrailingCommaInSinglelineFixer;
+use PhpCsFixer\Fixer\Basic\OctalNotationFixer;
 use PhpCsFixer\Fixer\Basic\PsrAutoloadingFixer;
 use PhpCsFixer\Fixer\Basic\SingleLineEmptyBodyFixer;
 use PhpCsFixer\Fixer\Casing\ClassReferenceNameCasingFixer;
@@ -244,6 +245,8 @@
             SingleLineEmptyBodyFixer::class, // Defined in PER 2.0
             // Values separated by a comma on a single line should not have a trailing comma.
             NoTrailingCommaInSinglelineFixer::class,
+            // Literal octal must be in 0o notation.
+            OctalNotationFixer::class,
             // Arrays should be formatted like function/method arguments
             TrimArraySpacesFixer::class,
             // In array declaration, there MUST be a whitespace after each comma
diff --git a/tests/Integration/Fixtures/NewPhpFeatures.correct.php.inc b/tests/Integration/Fixtures/NewPhpFeatures.correct.php.inc
index bff038b..e823f58 100644
--- a/tests/Integration/Fixtures/NewPhpFeatures.correct.php.inc
+++ b/tests/Integration/Fixtures/NewPhpFeatures.correct.php.inc
@@ -43,4 +43,10 @@ class NewPhpFeatures
         string $foo,
         string $bar,
     ): void {}
+
+    public function php81features(): void
+    {
+        // OctalNotationFixer
+        $numberInOctalNotation = 0o0123;
+    }
 }
diff --git a/tests/Integration/Fixtures/NewPhpFeatures.wrong.php.inc b/tests/Integration/Fixtures/NewPhpFeatures.wrong.php.inc
index 5629c7a..a73ba14 100644
--- a/tests/Integration/Fixtures/NewPhpFeatures.wrong.php.inc
+++ b/tests/Integration/Fixtures/NewPhpFeatures.wrong.php.inc
@@ -44,4 +44,10 @@ class NewPhpFeatures
         #[ParamAttribute] #[AnotherAttribute('foo')] string $foo,
         string $bar,
     ): void {}
+
+    public function php81features(): void
+    {
+        // OctalNotationFixer
+        $numberInOctalNotation = 0123;
+    }
 }