diff --git a/scripts/daemon/phabricator_daemon_launcher.php b/scripts/daemon/phabricator_daemon_launcher.php
index 4267a3a3c7..5fe297a6cd 100755
--- a/scripts/daemon/phabricator_daemon_launcher.php
+++ b/scripts/daemon/phabricator_daemon_launcher.php
@@ -85,7 +85,7 @@ switch (isset($argv[1]) ? $argv[1] : 'help') {
         $phid = $repository->getPHID();
 
         switch ($repository->getVersionControlSystem()) {
-          case 'git':
+          case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
             echo "Launching 'git fetch' daemon on the {$desc} repository...\n";
             $control->launchDaemon(
               'PhabricatorRepositoryGitFetchDaemon',
@@ -99,7 +99,7 @@ switch (isset($argv[1]) ? $argv[1] : 'help') {
                 $phid,
               ));
             break;
-          case 'svn':
+          case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
             echo "Launching discovery daemon on the {$desc} repository...\n";
             $control->launchDaemon(
               'PhabricatorRepositorySvnCommitDiscoveryDaemon',
@@ -107,6 +107,21 @@ switch (isset($argv[1]) ? $argv[1] : 'help') {
                 $phid,
               ));
             break;
+          case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
+            echo "Launching 'hg pull' daemon on the {$desc} repository...\n";
+            $control->launchDaemon(
+              'PhabricatorRepositoryMercurialPullDaemon',
+              array(
+                $phid,
+              ));
+            echo "Launching discovery daemon on the {$desc} repository...\n";
+            $control->launchDaemon(
+              'PhabricatorRepositoryMercurialCommitDiscoveryDaemon',
+              array(
+                $phid,
+              ));
+            break;
+
         }
       }
 
diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index fc28cb30f0..1436e99dae 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -578,6 +578,7 @@ phutil_register_library_map(array(
     'PhabricatorRepositoryGitHubNotification' => 'applications/repository/storage/githubnotification',
     'PhabricatorRepositoryGitHubPostReceiveController' => 'applications/repository/controller/github-post-receive',
     'PhabricatorRepositoryListController' => 'applications/repository/controller/list',
+    'PhabricatorRepositoryMercurialCommitDiscoveryDaemon' => 'applications/repository/daemon/commitdiscovery/mercurial',
     'PhabricatorRepositoryMercurialPullDaemon' => 'applications/repository/daemon/mercurialpull',
     'PhabricatorRepositoryPullLocalDaemon' => 'applications/repository/daemon/pulllocal',
     'PhabricatorRepositoryShortcut' => 'applications/repository/storage/shortcut',
@@ -1178,6 +1179,7 @@ phutil_register_library_map(array(
     'PhabricatorRepositoryGitHubNotification' => 'PhabricatorRepositoryDAO',
     'PhabricatorRepositoryGitHubPostReceiveController' => 'PhabricatorRepositoryController',
     'PhabricatorRepositoryListController' => 'PhabricatorRepositoryController',
+    'PhabricatorRepositoryMercurialCommitDiscoveryDaemon' => 'PhabricatorRepositoryCommitDiscoveryDaemon',
     'PhabricatorRepositoryMercurialPullDaemon' => 'PhabricatorRepositoryPullLocalDaemon',
     'PhabricatorRepositoryPullLocalDaemon' => 'PhabricatorRepositoryDaemon',
     'PhabricatorRepositoryShortcut' => 'PhabricatorRepositoryDAO',
diff --git a/src/applications/repository/daemon/commitdiscovery/mercurial/PhabricatorRepositoryMercurialCommitDiscoveryDaemon.php b/src/applications/repository/daemon/commitdiscovery/mercurial/PhabricatorRepositoryMercurialCommitDiscoveryDaemon.php
new file mode 100644
index 0000000000..01de317162
--- /dev/null
+++ b/src/applications/repository/daemon/commitdiscovery/mercurial/PhabricatorRepositoryMercurialCommitDiscoveryDaemon.php
@@ -0,0 +1,138 @@
+<?php
+
+/*
+ * Copyright 2011 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+class PhabricatorRepositoryMercurialCommitDiscoveryDaemon
+  extends PhabricatorRepositoryCommitDiscoveryDaemon {
+
+  protected function discoverCommits() {
+    $repository = $this->getRepository();
+
+    $vcs = $repository->getVersionControlSystem();
+    if ($vcs != PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL) {
+      throw new Exception("Repository is not a Mercurial repository.");
+    }
+
+    $repository_phid = $repository->getPHID();
+
+    $repo_base = $repository->getDetail('local-path');
+    list($stdout) = $repository->execxLocalCommand('branches');
+
+    $branches = ArcanistMercurialParser::parseMercurialBranches($stdout);
+    $got_something = false;
+    foreach ($branches as $name => $branch) {
+      $commit = $branch['rev'];
+      $commit = $this->getFullHash($commit);
+      if ($this->isKnownCommit($commit)) {
+        continue;
+      } else {
+        $this->discoverCommit($commit);
+        $got_something = true;
+      }
+    }
+
+    return $got_something;
+  }
+
+  private function getFullHash($commit) {
+
+    // NOTE: Mercurial shortens hashes to 12 characters by default. This
+    // implies collisions with as few as a few million commits. The
+    // documentation sensibly advises "Do not use short-form IDs for
+    // long-lived representations". It then continues "You can use the
+    // --debug option to display the full changeset ID". What?! Yes, this
+    // is in fact the only way to turn on full hashes, and the hg source
+    // code is littered with "hexfn = ui.debugflag and hex or short" and
+    // similar. There is no more-selective flag or config option.
+    //
+    // Unfortunately, "hg --debug" turns on tons of other extra output,
+    // including full commit messages in "hg log" and "hg parents" (which
+    // ignore --style); this renders them unparseable. So we have to use
+    // "hg id" to convert short hashes into full hashes. See:
+    //
+    // <http://mercurial.selenic.com/wiki/ChangeSetID>
+    //
+    // Of course, this means that if there are collisions we will break here
+    // (the short commit identifier won't be unambiguous) but maybe Mercurial
+    // will have a --full-hashes flag or something by then and we can fix it
+    // properly. Until we run into that, this allows us to store data in the
+    // right format so when we eventually encounter this we won't have to
+    // reparse every Mercurial repository.
+
+    $repository = $this->getRepository();
+    list($stdout) = $repository->execxLocalCommand(
+      'id --debug -i --rev %s',
+      $commit);
+    return trim($stdout);
+  }
+
+  private function discoverCommit($commit) {
+    $discover = array();
+    $insert = array();
+
+    $repository = $this->getRepository();
+
+    $discover[] = $commit;
+    $insert[] = $commit;
+
+    $seen_parent = array();
+
+    // For all the new commits at the branch heads, walk backward until we find
+    // only commits we've aleady seen.
+    while (true) {
+      $target = array_pop($discover);
+      list($stdout) = $repository->execxLocalCommand(
+        'parents --style default --rev %s',
+        $target);
+      $parents = ArcanistMercurialParser::parseMercurialLog($stdout);
+      if ($parents) {
+        foreach ($parents as $parent) {
+          $parent_commit = $parent['rev'];
+          $parent_commit = $this->getFullHash($parent_commit);
+          if (isset($seen_parent[$parent_commit])) {
+            continue;
+          }
+          $seen_parent[$parent_commit] = true;
+          if (!$this->isKnownCommit($parent_commit)) {
+            $discover[] = $parent_commit;
+            $insert[] = $parent_commit;
+          }
+        }
+      }
+      if (empty($discover)) {
+        break;
+      }
+      $this->stillWorking();
+    }
+
+    while (true) {
+      $target = array_pop($insert);
+      list($stdout) = $repository->execxLocalCommand(
+        'log --rev %s --template %s',
+        $target,
+        '{date|rfc822date}');
+      $epoch = strtotime($stdout);
+
+      $this->recordCommit($target, $epoch);
+
+      if (empty($insert)) {
+        break;
+      }
+    }
+  }
+
+}
diff --git a/src/applications/repository/daemon/commitdiscovery/mercurial/__init__.php b/src/applications/repository/daemon/commitdiscovery/mercurial/__init__.php
new file mode 100644
index 0000000000..e18b3c3941
--- /dev/null
+++ b/src/applications/repository/daemon/commitdiscovery/mercurial/__init__.php
@@ -0,0 +1,15 @@
+<?php
+/**
+ * This file is automatically generated. Lint this module to rebuild it.
+ * @generated
+ */
+
+
+
+phutil_require_module('arcanist', 'repository/parser/mercurial');
+
+phutil_require_module('phabricator', 'applications/repository/constants/repositorytype');
+phutil_require_module('phabricator', 'applications/repository/daemon/commitdiscovery/base');
+
+
+phutil_require_source('PhabricatorRepositoryMercurialCommitDiscoveryDaemon.php');