diff --git a/.changelog/conservative-parameter-commas.md b/.changelog/conservative-parameter-commas.md
new file mode 100644
index 0000000..e2366f6
--- /dev/null
+++ b/.changelog/conservative-parameter-commas.md
@@ -0,0 +1,6 @@
+---
+category: fixed
+type: patch
+---
+
+Avoid introducing PHP 8.0 parameter-list commas from the formatter's host runtime by default; preserve native consumer overrides and existing commas.
diff --git a/docs/resolved-preset.md b/docs/resolved-preset.md
index ce12534..daf567b 100644
--- a/docs/resolved-preset.md
+++ b/docs/resolved-preset.md
@@ -79,7 +79,7 @@ updating the fixture; do not regenerate it merely to silence a failure.
 | `switch_case_semicolon_to_colon` | `default` |
 | `switch_case_space` | `default` |
 | `ternary_operator_spaces` | `default` |
-| `trailing_comma_in_multiline` | `{"after_heredoc":true,"elements":["arguments","array_destructuring","arrays","match","parameters"]}` |
+| `trailing_comma_in_multiline` | `{"after_heredoc":true,"elements":["arguments","array_destructuring","arrays","match"]}` |
 | `types_spaces` | `default` |
 | `unary_operator_spaces` | `{"only_dec_inc":true}` |
 
@@ -89,6 +89,28 @@ must not be presented as proof that broader profiles are safe. Native ECS builde
 `withSkip()` replaces the builder’s skip list, while configured rules of the same
 class use the last configuration. Consumers own their explicit overrides.
 
+## Consumer language compatibility
+
+The formatter's PHP runtime is separate from the consumer's supported PHP versions.
+The default deliberately excludes `parameters` from the native multiline trailing
+comma rule: commas in parameter declarations require PHP 8.0, while running the
+formatter on PHP 8.3 or later does not authorize upgrading a consumer's syntax.
+Arguments, arrays, destructuring and match retain the selected native behavior,
+including `after_heredoc`. Existing parameter commas are preserved, not removed.
+This conservative exception is not a complete PER conformance claim or a PHP 7.4
+compatibility certification. Syntax checks use the executing PHP binary.
+
+A consumer that has reviewed PHP 8.0-or-later compatibility can explicitly include
+`parameters` through `ECSConfig::configure()`'s native callback. The callback runs
+last; it owns the complete `TrailingCommaInMultilineFixer` configuration supplied
+through `withConfiguredRule()`. No target version is inferred from the host.
+Explicit target selection and execution on consumer PHP versions remain part of
+the open compatibility and policy work in issues #2 and #5.
+
+Sources: [PHP parameter syntax](https://www.php.net/manual/en/functions.arguments.php),
+[native fixer options](https://cs.symfony.com/doc/rules/control_structure/trailing_comma_in_multiline.html),
+and [PER language-version exceptions](https://www.php-fig.org/per/coding-style/#previous-language-versions).
+
 Golden fixtures prove formatting, check-without-writes, exact fixed bytes and
 second-pass idempotence. Preservation covers author/package/typed-parameter/
 void-return documentation, property visibility, mutable DateTime construction
diff --git a/src/Config/ECSConfig.php b/src/Config/ECSConfig.php
index 81d6701..873a764 100644
--- a/src/Config/ECSConfig.php
+++ b/src/Config/ECSConfig.php
@@ -4,6 +4,7 @@
 
 namespace FastForward\CodeStandards\Config;
 
+use PhpCsFixer\Fixer\ControlStructure\TrailingCommaInMultilineFixer;
 use PhpCsFixer\Fixer\FunctionNotation\MethodArgumentSpaceFixer;
 use PhpCsFixer\Fixer\Phpdoc\GeneralPhpdocAnnotationRemoveFixer;
 use PhpCsFixer\Fixer\Phpdoc\NoEmptyPhpdocFixer;
@@ -33,6 +34,10 @@ public static function configure(?callable $customize = null): ECSConfigBuilder
                 PhpdocNoEmptyReturnFixer::class,
                 GeneralPhpdocAnnotationRemoveFixer::class,
             ])
+            ->withConfiguredRule(TrailingCommaInMultilineFixer::class, [
+                'after_heredoc' => true,
+                'elements' => ['arguments', 'array_destructuring', 'arrays', 'match'],
+            ])
             ->withConfiguredRule(MethodArgumentSpaceFixer::class, ['on_multiline' => 'ignore'])
             ->withConfiguredRule(PhpdocAlignFixer::class, ['align' => 'left'])
             ->withCache(self::cacheDirectory())
diff --git a/tests/Fixtures/consumer-language.php.inc b/tests/Fixtures/consumer-language.php.inc
new file mode 100644
index 0000000..28dcdb5
--- /dev/null
+++ b/tests/Fixtures/consumer-language.php.inc
@@ -0,0 +1,27 @@
+<?php
+
+function example(
+    int $count,
+    ?string $name = null
+): array {
+    return [
+        'array value'
+    ];
+}
+
+function existingComma(
+    string $name,
+): void {
+    consume(
+        'argument value'
+    );
+}
+
+function typedOnly(
+    int $count,
+    string $label
+): void {
+}
+
+(new Example())->run();
+(new class() {})->run();
diff --git a/tests/Fixtures/preset-rules.json b/tests/Fixtures/preset-rules.json
index 1d7e4dc..7abcf0e 100644
--- a/tests/Fixtures/preset-rules.json
+++ b/tests/Fixtures/preset-rules.json
@@ -393,8 +393,7 @@
                     "arguments",
                     "array_destructuring",
                     "arrays",
-                    "match",
-                    "parameters"
+                    "match"
                 ]
             },
             "risky": false
diff --git a/tests/Integration/StandardsTest.php b/tests/Integration/StandardsTest.php
index fbaf3c3..176caec 100644
--- a/tests/Integration/StandardsTest.php
+++ b/tests/Integration/StandardsTest.php
@@ -156,6 +156,72 @@ public function testStyleCheckDoesNotWriteAndExplicitFixIsIdempotent(): void
         self::assertSame($fixed, file_get_contents($this->directory . '/' . $path));
     }
 
+    /** Preserves older parameter syntax by default, existing commas and explicit fix/check boundaries. */
+    public function testDefaultFormattingDoesNotIntroduceParameterCommasFromTheHostRuntime(): void
+    {
+        $source = file_get_contents(__DIR__ . '/../Fixtures/consumer-language.php.inc');
+        $this->put('source.php', $source);
+        $this->commit();
+
+        $check = $this->cli(['check', '--all']);
+        self::assertSame(2, $check->getExitCode(), $check->getOutput() . $check->getErrorOutput());
+        self::assertSame($source, file_get_contents($this->directory . '/source.php'));
+        self::assertSame(['source.php'], $this->trackedAndUntrackedSources());
+
+        $fix = $this->cli(['fix', '--all']);
+        self::assertSame(0, $fix->getExitCode(), $fix->getOutput() . $fix->getErrorOutput());
+        $fixed = file_get_contents($this->directory . '/source.php');
+        self::assertStringContainsString("?string \$name = null\n", $fixed);
+        self::assertStringContainsString("string \$label\n", $fixed);
+        self::assertStringContainsString("string \$name,\n", $fixed);
+        self::assertStringContainsString("'array value',\n", $fixed);
+        self::assertStringContainsString("'argument value',\n", $fixed);
+        self::assertStringContainsString('(new Example())->run();', $fixed);
+        self::assertStringContainsString('(new class', $fixed);
+        self::assertStringContainsString('})->run();', $fixed);
+
+        foreach (['check', 'fix', 'check'] as $command) {
+            $result = $this->cli([$command, '--all']);
+            self::assertSame(0, $result->getExitCode(), $result->getOutput() . $result->getErrorOutput());
+            self::assertSame($fixed, file_get_contents($this->directory . '/source.php'));
+        }
+    }
+
+    /** Allows an explicitly reviewed native override to select parameter commas for PHP 8.0 or later. */
+    public function testConsumerCanExplicitlyOverrideTheConservativeParameterCommaPolicy(): void
+    {
+        $source = file_get_contents(__DIR__ . '/../Fixtures/consumer-language.php.inc');
+        $this->put('source.php', $source);
+        $this->put('.build/ecs.php', <<<'PHP'
+<?php
+
+return \FastForward\CodeStandards\Config\ECSConfig::configure(
+    static function (\Symplify\EasyCodingStandard\Configuration\ECSConfigBuilder $config): void {
+        $config->withConfiguredRule(
+            \PhpCsFixer\Fixer\ControlStructure\TrailingCommaInMultilineFixer::class,
+            ['after_heredoc' => true, 'elements' => ['parameters']],
+        );
+    },
+);
+PHP);
+        $this->commit();
+
+        $check = $this->cli(['check', '--all', '--config=.build/ecs.php']);
+        self::assertSame(2, $check->getExitCode(), $check->getOutput() . $check->getErrorOutput());
+        self::assertSame($source, file_get_contents($this->directory . '/source.php'));
+
+        $fix = $this->cli(['fix', '--all', '--config=.build/ecs.php']);
+        self::assertSame(0, $fix->getExitCode(), $fix->getOutput() . $fix->getErrorOutput());
+        $fixed = file_get_contents($this->directory . '/source.php');
+        self::assertStringContainsString("?string \$name = null,\n", $fixed);
+        self::assertStringContainsString("string \$label,\n", $fixed);
+        self::assertStringNotContainsString("'array value',\n", $fixed);
+        self::assertStringNotContainsString("'argument value',\n", $fixed);
+        self::assertSame(0, $this->cli(['check', '--all', '--config=.build/ecs.php'])->getExitCode());
+        self::assertSame(0, $this->cli(['fix', '--all', '--config=.build/ecs.php'])->getExitCode());
+        self::assertSame($fixed, file_get_contents($this->directory . '/source.php'));
+    }
+
     /** Proves parsing never executes selected source and syntax failures leave its bytes intact. */
     public function testSyntaxIsParsedWithoutExecutingSource(): void
     {