diff --git a/resources/sql/patches/011.badcommit.sql b/resources/sql/patches/011.badcommit.sql
new file mode 100644
index 0000000000..4ec76332b0
--- /dev/null
+++ b/resources/sql/patches/011.badcommit.sql
@@ -0,0 +1,44 @@
+CREATE DATABASE phabricator_herald;
+
+CREATE TABLE phabricator_herald.herald_action (
+  id int unsigned not null auto_increment primary key,
+  ruleID int unsigned not null,
+  action varchar(255) not null,
+  target text not null
+);
+
+CREATE TABLE phabricator_herald.herald_rule (
+  id int unsigned not null auto_increment primary key,
+  name varchar(255) not null,
+  authorPHID varchar(64) binary not null,
+  contentType varchar(255) not null,
+  mustMatchAll bool not null,
+  configVersion int unsigned not null default '1',
+  dateCreated int unsigned not null,
+  dateModified int unsigned not null,
+  unique key (authorPHID, name)
+);
+
+CREATE TABLE phabricator_herald.herald_condition (
+  id int unsigned not null auto_increment primary key,
+  ruleID int unsigned not null,
+  fieldName varchar(255) not null,
+  fieldCondition varchar(255) not null,
+  value text not null
+);
+
+CREATE TABLE phabricator_herald.herald_transcript (
+  id int unsigned not null auto_increment primary key,
+  phid varchar(64) binary not null,
+  time int unsigned not null,
+  host varchar(255) not null,
+  psth varchar(255) not null,
+  duration float not null,
+  objectPHID varchar(64) binary not null,
+  dryRun bool not null,
+  objectTranscript longblob not null,
+  ruleTranscripts longblob not null,
+  conditionTranscripts longblob not null,
+  applyTranscripts longblob not null,
+  unique key (phid)
+);
\ No newline at end of file
diff --git a/src/applications/diffusion/controller/commit/DiffusionCommitController.php b/src/applications/diffusion/controller/commit/DiffusionCommitController.php
index 11a754c9ec..0c62de6e0a 100644
--- a/src/applications/diffusion/controller/commit/DiffusionCommitController.php
+++ b/src/applications/diffusion/controller/commit/DiffusionCommitController.php
@@ -30,6 +30,12 @@ class DiffusionCommitController extends DiffusionController {
 
     $repository = $drequest->getRepository();
     $commit = $drequest->loadCommit();
+
+    if (!$commit) {
+      // TODO: Make more user-friendly.
+      throw new Exception('This commit has not parsed yet.');
+    }
+
     $commit_data = $drequest->loadCommitData();
 
     require_celerity_resource('diffusion-commit-view-css');
@@ -70,19 +76,38 @@ class DiffusionCommitController extends DiffusionController {
 
     $count = number_format(count($changes));
 
-    $change_panel = new AphrontPanelView();
-    $change_panel->setHeader("Changes ({$count})");
-    $change_panel->appendChild($change_table);
+    $bad_commit = null;
+    if ($count == 0) {
+      $bad_commit = queryfx_one(
+        id(new PhabricatorRepository())->establishConnection('r'),
+        'SELECT * FROM %T WHERE fullCommitName = %s',
+        PhabricatorRepository::TABLE_BADCOMMIT,
+        'r'.$repository->getCallsign().$commit->getCommitIdentifier());
+    }
 
-    $content[] = $change_panel;
+    if ($bad_commit) {
+      $error_panel = new AphrontErrorView();
+      $error_panel->setWidth(AphrontErrorView::WIDTH_WIDE);
+      $error_panel->setTitle('Bad Commit');
+      $error_panel->appendChild(
+        phutil_escape_html($bad_commit['description']));
 
+      $content[] = $error_panel;
+    } else {
+      $change_panel = new AphrontPanelView();
+      $change_panel->setHeader("Changes ({$count})");
+      $change_panel->appendChild($change_table);
 
-    $change_list =
-      '<div style="margin: 2em; color: #666; padding: 1em; background: #eee;">'.
-        '(list of changes goes here)'.
-      '</div>';
+      $content[] = $change_panel;
 
-    $content[] = $change_list;
+      $change_list =
+        '<div style="margin: 2em; color: #666; padding: 1em;
+          background: #eee;">'.
+          '(list of changes goes here)'.
+        '</div>';
+
+      $content[] = $change_list;
+    }
 
     return $this->buildStandardPageResponse(
       $content,
diff --git a/src/applications/diffusion/controller/commit/__init__.php b/src/applications/diffusion/controller/commit/__init__.php
index 0abf62d921..6e629ab204 100644
--- a/src/applications/diffusion/controller/commit/__init__.php
+++ b/src/applications/diffusion/controller/commit/__init__.php
@@ -9,10 +9,14 @@
 phutil_require_module('phabricator', 'applications/diffusion/controller/base');
 phutil_require_module('phabricator', 'applications/diffusion/query/pathchange/base');
 phutil_require_module('phabricator', 'applications/diffusion/view/commitchangetable');
+phutil_require_module('phabricator', 'applications/repository/storage/repository');
 phutil_require_module('phabricator', 'infrastructure/celerity/api');
+phutil_require_module('phabricator', 'storage/queryfx');
+phutil_require_module('phabricator', 'view/form/error');
 phutil_require_module('phabricator', 'view/layout/panel');
 
 phutil_require_module('phutil', 'markup');
+phutil_require_module('phutil', 'utils');
 
 
 phutil_require_source('DiffusionCommitController.php');
diff --git a/src/applications/repository/storage/repository/PhabricatorRepository.php b/src/applications/repository/storage/repository/PhabricatorRepository.php
index 8212b4bff0..ec2e0f1059 100644
--- a/src/applications/repository/storage/repository/PhabricatorRepository.php
+++ b/src/applications/repository/storage/repository/PhabricatorRepository.php
@@ -22,6 +22,7 @@ class PhabricatorRepository extends PhabricatorRepositoryDAO {
   const TABLE_PATHCHANGE = 'repository_pathchange';
   const TABLE_FILESYSTEM = 'repository_filesystem';
   const TABLE_SUMMARY = 'repository_summary';
+  const TABLE_BADCOMMIT = 'repository_badcommit';
 
   protected $phid;
   protected $name;
diff --git a/src/applications/repository/worker/base/PhabricatorRepositoryCommitParserWorker.php b/src/applications/repository/worker/base/PhabricatorRepositoryCommitParserWorker.php
index 19346397b0..fc23edac0f 100644
--- a/src/applications/repository/worker/base/PhabricatorRepositoryCommitParserWorker.php
+++ b/src/applications/repository/worker/base/PhabricatorRepositoryCommitParserWorker.php
@@ -84,4 +84,16 @@ abstract class PhabricatorRepositoryCommitParserWorker
     return new SimpleXMLElement($xml);
   }
 
+  protected function isBadCommit($full_commit_name) {
+    $repository = new PhabricatorRepository();
+
+    $bad_commit = queryfx_one(
+      $repository->establishConnection('w'),
+      'SELECT * FROM %T WHERE fullCommitName = %s',
+      PhabricatorRepository::TABLE_BADCOMMIT,
+      $full_commit_name);
+
+    return (bool)$bad_commit;
+  }
+
 }
diff --git a/src/applications/repository/worker/base/__init__.php b/src/applications/repository/worker/base/__init__.php
index ff7c96282d..d78aaa2839 100644
--- a/src/applications/repository/worker/base/__init__.php
+++ b/src/applications/repository/worker/base/__init__.php
@@ -9,6 +9,7 @@
 phutil_require_module('phabricator', 'applications/repository/storage/commit');
 phutil_require_module('phabricator', 'applications/repository/storage/repository');
 phutil_require_module('phabricator', 'infrastructure/daemon/workers/worker');
+phutil_require_module('phabricator', 'storage/queryfx');
 
 phutil_require_module('phutil', 'future/exec');
 phutil_require_module('phutil', 'parser/uri');
diff --git a/src/applications/repository/worker/commitchangeparser/git/PhabricatorRepositoryGitCommitChangeParserWorker.php b/src/applications/repository/worker/commitchangeparser/git/PhabricatorRepositoryGitCommitChangeParserWorker.php
index 8baa3d5f6d..b3d504f1a1 100644
--- a/src/applications/repository/worker/commitchangeparser/git/PhabricatorRepositoryGitCommitChangeParserWorker.php
+++ b/src/applications/repository/worker/commitchangeparser/git/PhabricatorRepositoryGitCommitChangeParserWorker.php
@@ -23,6 +23,13 @@ class PhabricatorRepositoryGitCommitChangeParserWorker
     PhabricatorRepository $repository,
     PhabricatorRepositoryCommit $commit) {
 
+    $full_name = 'r'.$repository->getCallsign().$commit->getCommitIdentifier();
+    echo "Parsing {$full_name}...\n";
+    if ($this->isBadCommit($full_name)) {
+      echo "This commit is marked bad!\n";
+      return;
+    }
+
     $local_path = $repository->getDetail('local-path');
 
     list($raw) = execx(
diff --git a/src/applications/repository/worker/commitchangeparser/svn/PhabricatorRepositorySvnCommitChangeParserWorker.php b/src/applications/repository/worker/commitchangeparser/svn/PhabricatorRepositorySvnCommitChangeParserWorker.php
index 8e55474a1d..fcbbf5b67c 100644
--- a/src/applications/repository/worker/commitchangeparser/svn/PhabricatorRepositorySvnCommitChangeParserWorker.php
+++ b/src/applications/repository/worker/commitchangeparser/svn/PhabricatorRepositorySvnCommitChangeParserWorker.php
@@ -44,7 +44,13 @@ class PhabricatorRepositorySvnCommitChangeParserWorker
     $svn_commit = $commit->getCommitIdentifier();
 
     $callsign = $repository->getCallsign();
-    echo "Parsing r{$callsign}{$svn_commit}...\n";
+    $full_name = 'r'.$callsign.$svn_commit;
+    echo "Parsing {$full_name}...\n";
+
+    if ($this->isBadCommit($full_name)) {
+      echo "This commit is marked bad!\n";
+      return;
+    }
 
     // Pull the top-level path changes out of "svn log". This is pretty
     // straightforward; just parse the XML log.