diff --git a/src/markup/__tests__/PhutilMarkupTestCase.php b/src/markup/__tests__/PhutilMarkupTestCase.php
index d333f4f..0197ab6 100644
--- a/src/markup/__tests__/PhutilMarkupTestCase.php
+++ b/src/markup/__tests__/PhutilMarkupTestCase.php
@@ -1,264 +1,265 @@
 <?php
 
 final class PhutilMarkupTestCase extends PhutilTestCase {
 
   public function testTagDefaults() {
     $this->assertEqual(
       (string)phutil_tag('br'),
       (string)phutil_tag('br', array()));
 
     $this->assertEqual(
       (string)phutil_tag('br', array()),
       (string)phutil_tag('br', array(), null));
   }
 
   public function testTagEmpty() {
     $this->assertEqual(
       '<br />',
       (string)phutil_tag('br', array(), null));
 
     $this->assertEqual(
       '<div></div>',
       (string)phutil_tag('div', array(), null));
 
     $this->assertEqual(
       '<div></div>',
       (string)phutil_tag('div', array(), ''));
   }
 
   public function testTagBasics() {
     $this->assertEqual(
       '<br />',
       (string)phutil_tag('br'));
 
     $this->assertEqual(
       '<div>y</div>',
       (string)phutil_tag('div', array(), 'y'));
   }
 
   public function testTagAttributes() {
     $this->assertEqual(
       '<div u="v">y</div>',
       (string)phutil_tag('div', array('u' => 'v'), 'y'));
 
     $this->assertEqual(
       '<br u="v" />',
       (string)phutil_tag('br', array('u' => 'v')));
   }
 
   public function testTagEscapes() {
     $this->assertEqual(
       '<br u="&lt;" />',
       (string)phutil_tag('br', array('u' => '<')));
 
     $this->assertEqual(
       '<div><br /></div>',
       (string)phutil_tag('div', array(), phutil_tag('br')));
   }
 
   public function testTagNullAttribute() {
     $this->assertEqual(
       '<br />',
       (string)phutil_tag('br', array('y' => null)));
   }
 
   public function testDefaultRelNoreferrer() {
     $map = array(
       // These should not have rel="nofollow" inserted implicitly.
       '/' => false,
       '/path/to/local.html' => false,
       '#example' => false,
       '' => false,
 
       // These should get the implicit insertion.
       'http://www.example.org/' => true,
       '///evil.com/' => true,
       '  http://www.example.org/' => true,
       'ftp://filez.com' => true,
       'mailto:santa@northpole.com' => true,
+      'tel:18005555555' => true,
     );
 
     foreach ($map as $input => $expect) {
       $tag = phutil_tag(
         'a',
         array(
           'href' => $input,
         ),
         'link');
       $tag = (string)$tag;
       $this->assertEqual($expect, (bool)preg_match('/noreferrer/', $tag));
     }
 
     // With an explicit `rel` present, we should not override it.
     $tag = phutil_tag(
       'a',
       array(
         'href' => 'http://www.example.org/',
         'rel' => 'nofollow',
       ),
       'link');
 
     $this->assertFalse((bool)preg_match('/noreferrer/', (string)$tag));
 
     // For tags other than `a`, we should not insert `rel`.
     $tag = phutil_tag(
       'link',
       array(
         'href' => 'http://www.example.org/',
       ),
       'link');
 
     $this->assertFalse((bool)preg_match('/noreferrer/', (string)$tag));
   }
 
 
   public function testTagJavascriptProtocolRejection() {
     $hrefs = array(
       'javascript:alert(1)'         => true,
       'JAVASCRIPT:alert(2)'         => true,
 
       // NOTE: When interpreted as a URI, this is dropped because of leading
       // whitespace.
       '     javascript:alert(3)'    => array(true, false),
       '/'                           => false,
       '/path/to/stuff/'             => false,
       ''                            => false,
       'http://example.com/'         => false,
       '#'                           => false,
       'javascript://anything'       => true,
 
       // Chrome 33 and IE11, at a minimum, treat this as Javascript.
       "javascript\n:alert(4)"       => true,
 
       // Opera currently accepts a variety of unicode spaces. This test case
       // has a smattering of them.
       "\xE2\x80\x89javascript:"     => true,
       "javascript\xE2\x80\x89:"     => true,
       "\xE2\x80\x84javascript:"     => true,
       "javascript\xE2\x80\x84:"     => true,
 
       // Because we're aggressive, all of unicode should trigger detection
       // by default.
       "\xE2\x98\x83javascript:"     => true,
       "javascript\xE2\x98\x83:"     => true,
       "\xE2\x98\x83javascript\xE2\x98\x83:" => true,
 
       // We're aggressive about this, so we'll intentionally raise false
       // positives in these cases.
       'javascript~:alert(5)'        => true,
       '!!!javascript!!!!:alert(6)'  => true,
 
       // However, we should raise true negatives in these slightly more
       // reasonable cases.
       'javascript/:docs.html'       => false,
       'javascripts:x.png'           => false,
       'COOLjavascript:page'         => false,
       '/javascript:alert(1)'        => false,
     );
 
     foreach (array(true, false) as $use_uri) {
       foreach ($hrefs as $href => $expect) {
         if (is_array($expect)) {
           $expect = ($use_uri ? $expect[1] : $expect[0]);
         }
 
         if ($use_uri) {
           $href = new PhutilURI($href);
         }
 
         $caught = null;
         try {
           phutil_tag('a', array('href' => $href), 'click for candy');
         } catch (Exception $ex) {
           $caught = $ex;
         }
         $this->assertEqual(
           $expect,
           $caught instanceof Exception,
           "Rejected href: {$href}");
       }
     }
   }
 
   public function testURIEscape() {
     $this->assertEqual(
       '%2B/%20%3F%23%26%3A%21xyz%25',
       phutil_escape_uri('+/ ?#&:!xyz%'));
   }
 
   public function testURIPathComponentEscape() {
     $this->assertEqual(
       'a%252Fb',
       phutil_escape_uri_path_component('a/b'));
 
     $str = '';
     for ($ii = 0; $ii <= 255; $ii++) {
       $str .= chr($ii);
     }
 
     $this->assertEqual(
       $str,
       phutil_unescape_uri_path_component(
         rawurldecode( // Simulates webserver.
           phutil_escape_uri_path_component($str))));
   }
 
   public function testHsprintf() {
     $this->assertEqual(
       '<div>&lt;3</div>',
       (string)hsprintf('<div>%s</div>', '<3'));
   }
 
   public function testAppendHTML() {
     $html = phutil_tag('hr');
     $html->appendHTML(phutil_tag('br'), '<evil>');
     $this->assertEqual('<hr /><br />&lt;evil&gt;', $html->getHTMLContent());
   }
 
   public function testArrayEscaping() {
     $this->assertEqual(
       '<div>&lt;div&gt;</div>',
       phutil_escape_html(
         array(
           hsprintf('<div>'),
           array(
             array(
               '<',
               array(
                 'd',
                 array(
                   array(
                     hsprintf('i'),
                   ),
                   'v',
                 ),
               ),
               array(
                 array(
                   '>',
                 ),
               ),
             ),
           ),
           hsprintf('</div>'),
         )));
 
     $this->assertEqual(
       '<div><br /><hr /><wbr /></div>',
       phutil_tag(
         'div',
         array(),
         array(
           array(
             array(
               phutil_tag('br'),
               array(
                 phutil_tag('hr'),
               ),
               phutil_tag('wbr'),
             ),
           ),
         ))->getHTMLContent());
   }
 
 }
diff --git a/src/markup/engine/__tests__/PhutilRemarkupEngineTestCase.php b/src/markup/engine/__tests__/PhutilRemarkupEngineTestCase.php
index 0547a5c..692f932 100644
--- a/src/markup/engine/__tests__/PhutilRemarkupEngineTestCase.php
+++ b/src/markup/engine/__tests__/PhutilRemarkupEngineTestCase.php
@@ -1,113 +1,114 @@
 <?php
 
 /**
  * Test cases for @{class:PhutilRemarkupEngine}.
  */
 final class PhutilRemarkupEngineTestCase extends PhutilTestCase {
 
   public function testEngine() {
     $root = dirname(__FILE__).'/remarkup/';
     foreach (Filesystem::listDirectory($root, $hidden = false) as $file) {
       $this->markupText($root.$file);
     }
   }
 
   private function markupText($markup_file) {
     $contents = Filesystem::readFile($markup_file);
     $file = basename($markup_file);
 
     $parts = explode("\n~~~~~~~~~~\n", $contents);
     $this->assertEqual(3, count($parts), $markup_file);
 
     list($input_remarkup, $expected_output, $expected_text) = $parts;
 
     $engine = $this->buildNewTestEngine();
 
     switch ($file) {
       case 'raw-escape.txt':
 
         // NOTE: Here, we want to test PhutilRemarkupEscapeRemarkupRule and
         // PhutilRemarkupBlockStorage, which are triggered by "\1". In the
         // test, "~" is used as a placeholder for "\1" since it's hard to type
         // "\1".
 
         $input_remarkup = str_replace('~', "\1", $input_remarkup);
         $expected_output = str_replace('~', "\1", $expected_output);
         $expected_text = str_replace('~', "\1", $expected_text);
         break;
       case 'toc.txt':
         $engine->setConfig('header.generate-toc', true);
         break;
     }
 
     $actual_output = (string)$engine->markupText($input_remarkup);
 
     switch ($file) {
       case 'toc.txt':
         $table_of_contents =
           PhutilRemarkupHeaderBlockRule::renderTableOfContents($engine);
         $actual_output = $table_of_contents."\n\n".$actual_output;
         break;
     }
 
     $this->assertEqual(
       $expected_output,
       $actual_output,
       "Failed to markup HTML in file '{$file}'.");
 
     $engine->setMode(PhutilRemarkupEngine::MODE_TEXT);
     $actual_output = (string)$engine->markupText($input_remarkup);
 
     $this->assertEqual(
       $expected_text,
       $actual_output,
       "Failed to markup text in file '{$file}'.");
   }
 
   private function buildNewTestEngine() {
     $engine = new PhutilRemarkupEngine();
     $engine->setConfig('uri.prefix', 'http://www.example.com/');
 
     $engine->setConfig(
       'uri.allowed-protocols',
       array(
         'http' => true,
         'mailto' => true,
+        'tel' => true,
       ));
 
     $rules = array();
     $rules[] = new PhutilRemarkupEscapeRemarkupRule();
     $rules[] = new PhutilRemarkupMonospaceRule();
     $rules[] = new PhutilRemarkupDocumentLinkRule();
     $rules[] = new PhutilRemarkupHyperlinkRule();
     $rules[] = new PhutilRemarkupBoldRule();
     $rules[] = new PhutilRemarkupItalicRule();
     $rules[] = new PhutilRemarkupDelRule();
     $rules[] = new PhutilRemarkupUnderlineRule();
 
     $blocks = array();
     $blocks[] = new PhutilRemarkupQuotesBlockRule();
     $blocks[] = new PhutilRemarkupReplyBlockRule();
     $blocks[] = new PhutilRemarkupHeaderBlockRule();
     $blocks[] = new PhutilRemarkupHorizontalRuleBlockRule();
     $blocks[] = new PhutilRemarkupCodeBlockRule();
     $blocks[] = new PhutilRemarkupLiteralBlockRule();
     $blocks[] = new PhutilRemarkupNoteBlockRule();
     $blocks[] = new PhutilRemarkupTableBlockRule();
     $blocks[] = new PhutilRemarkupSimpleTableBlockRule();
     $blocks[] = new PhutilRemarkupDefaultBlockRule();
     $blocks[] = new PhutilRemarkupListBlockRule();
     $blocks[] = new PhutilRemarkupInterpreterBlockRule();
 
     foreach ($blocks as $block) {
       if (!($block instanceof PhutilRemarkupCodeBlockRule)) {
         $block->setMarkupRules($rules);
       }
     }
 
     $engine->setBlockRules($blocks);
 
     return $engine;
   }
 
 }
diff --git a/src/markup/engine/__tests__/remarkup/link-tel.txt b/src/markup/engine/__tests__/remarkup/link-tel.txt
new file mode 100644
index 0000000..aac13c2
--- /dev/null
+++ b/src/markup/engine/__tests__/remarkup/link-tel.txt
@@ -0,0 +1,18 @@
+[[ tel:18005555555 | call me ]]
+
+[ call me ]( tel:18005555555 )
+
+[[tel:18005555555]]
+
+~~~~~~~~~~
+<p><a href="tel:18005555555" class="remarkup-link" target="_blank" rel="noreferrer">call me</a></p>
+
+<p><a href="tel:18005555555" class="remarkup-link" target="_blank" rel="noreferrer">call me</a></p>
+
+<p><a href="tel:18005555555" class="remarkup-link" target="_blank" rel="noreferrer">18005555555</a></p>
+~~~~~~~~~~
+call me <18005555555>
+
+call me <18005555555>
+
+18005555555
diff --git a/src/markup/engine/remarkup/markuprule/PhutilRemarkupDocumentLinkRule.php b/src/markup/engine/remarkup/markuprule/PhutilRemarkupDocumentLinkRule.php
index 0d5debf..bbd23be 100644
--- a/src/markup/engine/remarkup/markuprule/PhutilRemarkupDocumentLinkRule.php
+++ b/src/markup/engine/remarkup/markuprule/PhutilRemarkupDocumentLinkRule.php
@@ -1,123 +1,124 @@
 <?php
 
 final class PhutilRemarkupDocumentLinkRule extends PhutilRemarkupRule {
 
   public function getPriority() {
     return 150.0;
   }
 
   public function apply($text) {
 
     // Handle mediawiki-style links: [[ href | name ]]
     $text = preg_replace_callback(
       '@\B\\[\\[([^|\\]]+)(?:\\|([^\\]]+))?\\]\\]\B@U',
       array($this, 'markupDocumentLink'),
       $text);
 
     // Handle markdown-style links: [name](href)
     $text = preg_replace_callback(
       '@\B\\[([^\\]]+)\\]\\(([^\\)]+)\\)\B@U',
       array($this, 'markupAlternateLink'),
       $text);
 
     return $text;
   }
 
   protected function renderHyperlink($link, $name) {
     if ($this->getEngine()->isTextMode()) {
       $text = $link;
       if (strncmp($link, '/', 1) == 0 || strncmp($link, '#', 1) == 0) {
         $base = $this->getEngine()->getConfig('uri.prefix');
         if (strncmp($link, '/', 1) == 0) {
           $base = rtrim($base, '/');
         }
         $text = $base.$text;
       }
 
-      // If present, strip off "mailto:".
-      $text = preg_replace('/^mailto:/', '', $text);
+      // If present, strip off "mailto:" or "tel:".
+      $text = preg_replace('/^(?:mailto|tel):/', '', $text);
 
       if ($link == $name) {
         return $text;
       }
       return $name.' <'.$text.'>';
     }
 
     // By default, we open links in a new window or tab. For anchors on the same
     // page, just jump normally.
     $target = '_blank';
     if (strncmp($link, '#', 1) == 0) {
       $target = null;
     }
 
-    $name = preg_replace('/^mailto:/', '', $name);
+    $name = preg_replace('/^(?:mailto|tel):/', '', $name);
 
     if ($this->getEngine()->getState('toc')) {
       return $name;
     } else {
       return phutil_tag(
         'a',
         array(
           'href'    => $link,
           'class'   => 'remarkup-link',
           'target'  => $target,
         ),
         $name);
     }
   }
 
   public function markupAlternateLink($matches) {
     $uri = trim($matches[2]);
 
     // NOTE: We apply some special rules to avoid false positives here. The
     // major concern is that we do not want to convert `x[0][1](y)` in a
     // discussion about C source code into a link. To this end, we:
     //
     //   - Don't match at word boundaries;
     //   - require the URI to contain a "/" character or "@" character; and
     //   - reject URIs which being with a quote character.
 
     if ($uri[0] == '"' || $uri[0] == "'" || $uri[0] == '`') {
       return $matches[0];
     }
 
     if (strpos($uri, '/') === false &&
-        strpos($uri, '@') === false) {
+        strpos($uri, '@') === false &&
+        strncmp($uri, 'tel:', 4)) {
       return $matches[0];
     }
 
     return $this->markupDocumentLink(
       array(
         $matches[0],
         $matches[2],
         $matches[1],
       ));
   }
 
   public function markupDocumentLink($matches) {
     $uri = trim($matches[1]);
     $name = trim(idx($matches, 2, $uri));
 
     // If whatever is being linked to begins with "/" or "#", or has "://",
-    // or is "mailto:", treat it as a URI instead of a wiki page.
-    $is_uri = preg_match('@(^/)|(://)|(^#)|(^mailto:)@', $uri);
+    // or is "mailto:" or "tel:", treat it as a URI instead of a wiki page.
+    $is_uri = preg_match('@(^/)|(://)|(^#)|(^(?:mailto|tel):)@', $uri);
 
     if ($is_uri && strncmp('/', $uri, 1) && strncmp('#', $uri, 1)) {
       $protocols = $this->getEngine()->getConfig(
         'uri.allowed-protocols',
         array());
       $protocol = id(new PhutilURI($uri))->getProtocol();
       if (!idx($protocols, $protocol)) {
         // Don't treat this as a URI if it's not an allowed protocol.
         $is_uri = false;
       }
     }
 
     if (!$is_uri) {
       return $matches[0];
     }
 
     return $this->getEngine()->storeText($this->renderHyperlink($uri, $name));
   }
 
 }