diff --git a/src/main/php/web/Headers.class.php b/src/main/php/web/Headers.class.php
index 3c492ec..a7162e4 100755
--- a/src/main/php/web/Headers.class.php
+++ b/src/main/php/web/Headers.class.php
@@ -11,6 +11,7 @@
  * @test  web.unittest.HeadersTest
  */
 abstract class Headers {
+  const ATTR_CHAR= 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.-_';
 
   /**
    * Formats a date for use in headers
@@ -162,6 +163,23 @@ protected function next($input, &$offset) {
             // consistency with PHP, see https://github.com/php/php-src/issues/8206
             $parameters[$name]= strtr(substr($input, $offset + 1, $p - $offset - 2), ['\"' => '"']);
             $offset= $p + 1;
+          } else if ('*' === $name[strlen($name) - 1]) {
+
+            // RFC 8187: Character Encoding and Language for HTTP Header Field Parameters
+            $s= strcspn($input, "'", $offset);
+            $charset= substr($input, $offset, $s);
+            $offset+= $s + 1;
+
+            $s= strcspn($input, "'", $offset);
+            $lang= substr($input, $offset, $s);
+            $offset+= $s + 1;
+
+            $s= strcspn($input, ',;', $offset);
+            $parameters[$name]= [
+              'lang'  => $lang ?: null,
+              'value' => iconv($charset, \xp::ENCODING, urldecode(substr($input, $offset, $s)))
+            ];
+            $offset+= $s + 1;
           } else {
             $s= strcspn($input, ',;', $offset);
             $parameters[$name]= substr($input, $offset, $s);
diff --git a/src/main/php/web/Parameterized.class.php b/src/main/php/web/Parameterized.class.php
index 149e8d6..9f261f3 100755
--- a/src/main/php/web/Parameterized.class.php
+++ b/src/main/php/web/Parameterized.class.php
@@ -7,28 +7,86 @@ class Parameterized {
    * Creates a new instance
    *
    * @param  string $value
-   * @param  [:string] $params
+   * @param  [:var] $params
    */
-  public function __construct($value, array $params) {
+  public function __construct($value, array $params= []) {
     $this->value= $value;
     $this->params= $params;
   }
 
+  /**
+   * Passes parameters and optionally, their ASCII equivalents.
+   *
+   * @param  string $name
+   * @param  string|[:string] $value
+   * @param  ?string $equivalent
+   * @return self
+   */
+  public function with($name, $value, $equivalent= null) {
+    $name= rtrim($name, '*');
+    null === $equivalent || $this->params[$name]= $equivalent;
+
+    if (is_array($value)) {
+      $this->params[$name.'*']= 1 === sizeof($value)
+        ? ['lang' => current($value), 'value' => key($value)]
+        : $value
+      ;
+    } else if (isset($equivalent) || preg_match('/[\x7f-\xff]/', $value)) {
+      $this->params[$name.'*']= ['lang' => null, 'value' => $value];
+    } else {
+      $this->params[$name]= $value;
+    }
+
+    return $this;
+  }
+
   /** @return string */
   public function value() { return $this->value; }
 
-  /** @return [:string] */
+  /** @return [:var] */
   public function params() { return $this->params; }
 
   /**
-   * Gets a parameter by its name, returning a default value if it's
-   * not present.
+   * Gets a parameter by its name, returning a default value if it's not
+   * present. Prefers the RFC 8187 encoded parameter ending with `*`.
    *
    * @param  string $name
    * @param  var $default
    * @return var
    */
   public function param($name, $default= null) {
+    if ($param= $this->params[$name.'*'] ?? null) {
+      return $param['value'];
+    } else {
+      return $this->params[$name] ?? $default;
+    }
+  }
+
+  /**
+   * Gets a parameter equivalent by its name, returning a default value
+   * if it's not present.
+   *
+   * @param  string $name
+   * @param  var $default
+   * @return var
+   */
+  public function equivalent($name, $default= null) {
     return $this->params[$name] ?? $default;
   }
+
+  /** @return string */
+  public function __toString() {
+    $s= $this->value;
+    foreach ($this->params as $name => $value) {
+      $s.= '; '.$name;
+      if (is_array($value)) {
+        $s.= "=UTF-8'{$value['lang']}'".rawurlencode($value['value']);
+      } else if (strspn($value, Headers::ATTR_CHAR) < strlen($value)) {
+        $s.= '="'.strtr($value, ['\\' => '\\\\', '"' => '\\"']).'"';
+      } else {
+        $s.= '='.$value;
+      }
+    }
+    return $s;
+  }
 }
\ No newline at end of file
diff --git a/src/test/php/web/unittest/HeadersTest.class.php b/src/test/php/web/unittest/HeadersTest.class.php
index ddfa04e..e838338 100755
--- a/src/test/php/web/unittest/HeadersTest.class.php
+++ b/src/test/php/web/unittest/HeadersTest.class.php
@@ -34,6 +34,38 @@ public function content_disposition($header) {
     );
   }
 
+  #[Test]
+  public function rfc8187_encoding() {
+    $parameterized= Headers::parameterized()->parse("attachment; filename*=UTF-8''%C3%BCber%20name.jpg");
+
+    Assert::equals('attachment', $parameterized->value());
+    Assert::equals(['filename*' => ['lang' => null, 'value' => 'über name.jpg']], $parameterized->params());
+    Assert::equals('über name.jpg', $parameterized->param('filename'));
+    Assert::null($parameterized->equivalent('filename'));
+  }
+
+  #[Test]
+  public function rfc8187_encoding_and_language() {
+    $parameterized= Headers::parameterized()->parse("attachment; filename*=UTF-8'en'file%20name.jpg");
+
+    Assert::equals('attachment', $parameterized->value());
+    Assert::equals(['filename*' => ['lang' => 'en', 'value' => 'file name.jpg']], $parameterized->params());
+    Assert::equals('file name.jpg', $parameterized->param('filename'));
+    Assert::null($parameterized->equivalent('filename'));
+  }
+
+  #[Test]
+  public function rfc8187_encoded_takes_precedence() {
+    $parameterized= Headers::parameterized()->parse("attachment; filename=\"ascii.jpg\"; filename*=UTF-8''unicode.jpg");
+
+    Assert::equals(
+      ['filename' => 'ascii.jpg', 'filename*' => ['lang' => null, 'value' => 'unicode.jpg']],
+      $parameterized->params()
+    );
+    Assert::equals('unicode.jpg', $parameterized->param('filename'));
+    Assert::equals('ascii.jpg', $parameterized->equivalent('filename'));
+  }
+
   #[Test, Values(['5;url=http://www.w3.org/pub/WWW/People.html', '5; url=http://www.w3.org/pub/WWW/People.html',])]
   public function refresh($header) {
     Assert::equals(
diff --git a/src/test/php/web/unittest/ResponseTest.class.php b/src/test/php/web/unittest/ResponseTest.class.php
index 13b9b4d..17137cc 100755
--- a/src/test/php/web/unittest/ResponseTest.class.php
+++ b/src/test/php/web/unittest/ResponseTest.class.php
@@ -6,19 +6,42 @@
 use test\{Assert, Expect, Test, Values};
 use util\URI;
 use web\io\{Buffered, TestOutput};
-use web\{Cookie, Response};
+use web\{Cookie, Response, Parameterized};
 
 class ResponseTest {
 
-  /**
-   * Assertion helper
-   *
-   * @param  string $expected
-   * @param  web.Response $response
-   * @throws unittest.AssertionFailedError
-   */
-  private function assertResponse($expected, $response) {
-    Assert::equals($expected, $response->output()->bytes());
+  /** @return iterable */
+  private function answers() {
+
+    // Supplied as-is
+    yield [200, 'OK', 'HTTP/1.1 200 OK'];
+    yield [404, 'Not Found', 'HTTP/1.1 404 Not Found'];
+
+    // Status message derived from code
+    yield [200, null, 'HTTP/1.1 200 OK'];
+    yield [404, null, 'HTTP/1.1 404 Not Found'];
+
+    // Status message overridden
+    yield [200, 'Okay', 'HTTP/1.1 200 Okay'];
+    yield [404, 'Nope', 'HTTP/1.1 404 Nope'];
+  }
+
+  /** @return iterable */
+  private function filenames() {
+
+    // Simple file names
+    yield ['test.txt', 'filename=test.txt'];
+    yield ['a b.txt', 'filename="a b.txt"'];
+    yield ['"hello".txt', 'filename="\"hello\".txt"'];
+    yield ['über.txt', "filename*=UTF-8''%C3%BCber.txt"];
+
+    // In the form of [name => lang]
+    yield [['test.txt' => null], "filename*=UTF-8''test.txt"];
+    yield [['über.txt' => null], "filename*=UTF-8''%C3%BCber.txt"];
+    yield [['über.txt' => 'de'], "filename*=UTF-8'de'%C3%BCber.txt"];
+
+    // As received from Parameterized::params()
+    yield [['lang' => 'de', 'value' => 'über.txt'], "filename*=UTF-8'de'%C3%BCber.txt"];
   }
 
   #[Test]
@@ -71,10 +94,7 @@ public function headers() {
     $res= new Response(new TestOutput());
     $res->header('Content-Type', 'text/plain');
     $res->header('Content-Length', '0');
-    Assert::equals(
-      ['Content-Type' => 'text/plain', 'Content-Length' => '0'],
-      $res->headers()
-    );
+    Assert::equals(['Content-Type' => 'text/plain', 'Content-Length' => '0'], $res->headers());
   }
 
   #[Test]
@@ -142,7 +162,7 @@ public function cookies() {
     Assert::equals($cookies, $res->cookies());
   }
 
-  #[Test, Values([[200, 'OK', 'HTTP/1.1 200 OK'], [404, 'Not Found', 'HTTP/1.1 404 Not Found'], [200, null, 'HTTP/1.1 200 OK'], [404, null, 'HTTP/1.1 404 Not Found'], [200, 'Okay', 'HTTP/1.1 200 Okay'], [404, 'Nope', 'HTTP/1.1 404 Nope']])]
+  #[Test, Values(from: 'answers')]
   public function answer($status, $message, $line) {
     $out= new TestOutput();
 
@@ -150,7 +170,7 @@ public function answer($status, $message, $line) {
     $res->answer($status, $message);
     $res->flush();
 
-    $this->assertResponse($line."\r\n\r\n", $res);
+    Assert::that($res->output()->bytes())->isEqualTo($line."\r\n\r\n");
   }
 
   #[Test]
@@ -167,7 +187,7 @@ public function hint() {
     $res->answer(200, 'OK');
     $res->flush();
 
-    $this->assertResponse("HTTP/1.1 100 Continue\r\n\r\nHTTP/1.1 200 OK\r\n\r\n", $res);
+    Assert::that($res->output()->bytes())->isEqualTo("HTTP/1.1 100 Continue\r\n\r\nHTTP/1.1 200 OK\r\n\r\n");
   }
 
   #[Test]
@@ -178,12 +198,11 @@ public function hint_with_headers() {
       'Connection' => 'Upgrade'
     ]);
 
-    $this->assertResponse(
+    Assert::that($res->output()->bytes())->isEqualTo(
       "HTTP/1.1 101 Switching Protocols\r\n".
       "Upgrade: websocket\r\n".
       "Connection: Upgrade\r\n".
-      "\r\n",
-      $res
+      "\r\n"
     );
   }
 
@@ -195,7 +214,7 @@ public function hint_uses_and_retains_previously_set_headers() {
     $res->answer(200, 'OK');
     $res->flush();
 
-    $this->assertResponse(
+    Assert::that($res->output()->bytes())->isEqualTo(
       "HTTP/1.1 103 Early Hints\r\n".
       "Link: </main.css>; rel=preload; as=style\r\n".
       "Link: </script.js>; rel=preload; as=script\r\n".
@@ -203,8 +222,7 @@ public function hint_uses_and_retains_previously_set_headers() {
       "HTTP/1.1 200 OK\r\n".
       "Link: </main.css>; rel=preload; as=style\r\n".
       "Link: </script.js>; rel=preload; as=script\r\n".
-      "\r\n",
-      $res
+      "\r\n"
     );
   }
 
@@ -215,7 +233,12 @@ public function send_headers() {
     $res->header('Content-Length', '0');
     $res->flush();
 
-    $this->assertResponse("HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\nContent-Length: 0\r\n\r\n", $res);
+    Assert::that($res->output()->bytes())->isEqualTo(
+      "HTTP/1.1 200 OK\r\n".
+      "Content-Type: text/plain\r\n".
+      "Content-Length: 0\r\n".
+      "\r\n"
+    );
   }
 
   #[Test]
@@ -223,10 +246,39 @@ public function send_html() {
     $res= new Response(new TestOutput());
     $res->send('<h1>Test</h1>', 'text/html');
 
-    $this->assertResponse(
+    Assert::that($res->output()->bytes())->isEqualTo(
       "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\nContent-Length: 13\r\n\r\n".
-      "<h1>Test</h1>",
-      $res
+      "<h1>Test</h1>"
+    );
+  }
+
+  #[Test, Values(from: 'filenames')]
+  public function send_file($name, $params) {
+    $res= new Response(new TestOutput());
+    $res->header('Content-Disposition', (new Parameterized('attachment'))->with('filename', $name));
+    $res->flush();
+
+    Assert::that($res->output()->bytes())->isEqualTo(
+      "HTTP/1.1 200 OK\r\n".
+      "Content-Disposition: attachment; {$params}\r\n".
+      "\r\n"
+    );
+  }
+
+  #[Test, Values(['uber.txt', 'über.txt'])]
+  public function send_file_rfc8187_with_ascii_equivalent($name) {
+    $res= new Response(new TestOutput());
+    $res->header('Content-Disposition', (new Parameterized('attachment'))->with(
+      'filename',
+      $name,
+      $equivalent= 'uber.txt'
+    ));
+    $res->flush();
+
+    Assert::that($res->output()->bytes())->isEqualTo(
+      "HTTP/1.1 200 OK\r\n".
+      "Content-Disposition: attachment; filename=uber.txt; filename*=UTF-8''".rawurlencode($name)."\r\n".
+      "\r\n"
     );
   }
 
@@ -235,10 +287,9 @@ public function transmit_stream_with_length() {
     $res= new Response(new TestOutput());
     foreach ($res->transmit(new MemoryInputStream('<h1>Test</h1>'), 'text/html', 13) as $_) { }
 
-    $this->assertResponse(
+    Assert::that($res->output()->bytes())->isEqualTo(
       "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\nContent-Length: 13\r\n\r\n".
-      "<h1>Test</h1>",
-      $res
+      "<h1>Test</h1>"
     );
   }
 
@@ -247,10 +298,9 @@ public function transmit_stream_chunked() {
     $res= new Response(new TestOutput());
     foreach ($res->transmit(new MemoryInputStream('<h1>Test</h1>'), 'text/html') as $_) { }
 
-    $this->assertResponse(
+    Assert::that($res->output()->bytes())->isEqualTo(
       "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\nTransfer-Encoding: chunked\r\n\r\n".
-      "d\r\n<h1>Test</h1>\r\n0\r\n\r\n",
-      $res
+      "d\r\n<h1>Test</h1>\r\n0\r\n\r\n"
     );
   }
 
@@ -259,10 +309,9 @@ public function transmit_stream_buffered() {
     $res= new Response(new TestOutput(Buffered::class));
     foreach ($res->transmit(new MemoryInputStream('<h1>Test</h1>'), 'text/html') as $_) { }
 
-    $this->assertResponse(
+    Assert::that($res->output()->bytes())->isEqualTo(
       "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\nContent-Length: 13\r\n\r\n".
-      "<h1>Test</h1>",
-      $res
+      "<h1>Test</h1>"
     );
   }
 
@@ -275,10 +324,9 @@ public function out() { /* Not implemented */ }
     };
     foreach ($res->transmit($channel, 'text/html', 13) as $_) { }
 
-    $this->assertResponse(
+    Assert::that($res->output()->bytes())->isEqualTo(
       "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\nContent-Length: 13\r\n\r\n".
-      "<h1>Test</h1>",
-      $res
+      "<h1>Test</h1>"
     );
   }
 
@@ -295,9 +343,11 @@ public function cookies_and_headers_are_merged() {
     $res->cookie(new Cookie('toggle', 'future'));
     $res->flush();
 
-    $this->assertResponse(
-      "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\nSet-Cookie: toggle=future; SameSite=Lax; HttpOnly\r\n\r\n",
-      $res
+    Assert::that($res->output()->bytes())->isEqualTo(
+      "HTTP/1.1 200 OK\r\n".
+      "Content-Type: text/html\r\n".
+      "Set-Cookie: toggle=future; SameSite=Lax; HttpOnly\r\n".
+      "\r\n"
     );
   }