diff --git a/resources/sql/autopatches/20180306.opath.03.purge.php b/resources/sql/autopatches/20180306.opath.03.purge.php
new file mode 100644
index 0000000000..91a15e2a58
--- /dev/null
+++ b/resources/sql/autopatches/20180306.opath.03.purge.php
@@ -0,0 +1,22 @@
+<?php
+
+$table = new PhabricatorOwnersPath();
+$conn = $table->establishConnection('w');
+
+$seen = array();
+foreach (new LiskMigrationIterator($table) as $path) {
+  $package_id = $path->getPackageID();
+  $repository_phid = $path->getRepositoryPHID();
+  $path_index = $path->getPathIndex();
+
+  if (!isset($seen[$package_id][$repository_phid][$path_index])) {
+    $seen[$package_id][$repository_phid][$path_index] = true;
+    continue;
+  }
+
+  queryfx(
+    $conn,
+    'DELETE FROM %T WHERE id = %d',
+    $table->getTableName(),
+    $path->getID());
+}
diff --git a/resources/sql/autopatches/20180306.opath.04.unique.sql b/resources/sql/autopatches/20180306.opath.04.unique.sql
new file mode 100644
index 0000000000..2349533b1f
--- /dev/null
+++ b/resources/sql/autopatches/20180306.opath.04.unique.sql
@@ -0,0 +1,2 @@
+ALTER TABLE {$NAMESPACE}_owners.owners_path
+  ADD UNIQUE KEY `key_path` (packageID, repositoryPHID, pathIndex);
diff --git a/src/applications/owners/storage/PhabricatorOwnersPath.php b/src/applications/owners/storage/PhabricatorOwnersPath.php
index 47f7faa2b3..7e7822df1a 100644
--- a/src/applications/owners/storage/PhabricatorOwnersPath.php
+++ b/src/applications/owners/storage/PhabricatorOwnersPath.php
@@ -1,117 +1,118 @@
 <?php
 
 final class PhabricatorOwnersPath extends PhabricatorOwnersDAO {
 
   protected $packageID;
   protected $repositoryPHID;
   protected $pathIndex;
   protected $path;
   protected $excluded;
 
   private $fragments;
   private $fragmentCount;
 
   protected function getConfiguration() {
     return array(
       self::CONFIG_TIMESTAMPS => false,
       self::CONFIG_COLUMN_SCHEMA => array(
         'path' => 'text255',
         'pathIndex' => 'bytes12',
         'excluded' => 'bool',
       ),
       self::CONFIG_KEY_SCHEMA => array(
-        'packageID' => array(
-          'columns' => array('packageID'),
+        'key_path' => array(
+          'columns' => array('packageID', 'repositoryPHID', 'pathIndex'),
+          'unique' => true,
         ),
       ),
     ) + parent::getConfiguration();
   }
 
   public static function newFromRef(array $ref) {
     $path = new PhabricatorOwnersPath();
     $path->repositoryPHID = $ref['repositoryPHID'];
 
     $raw_path = $ref['path'];
 
     $path->pathIndex = PhabricatorHash::digestForIndex($raw_path);
     $path->path = $raw_path;
 
     $path->excluded = $ref['excluded'];
 
     return $path;
   }
 
   public function getRef() {
     return array(
       'repositoryPHID' => $this->getRepositoryPHID(),
       'path' => $this->getPath(),
       'excluded' => (int)$this->getExcluded(),
     );
   }
 
   public static function getTransactionValueChanges(array $old, array $new) {
     return array(
       self::getTransactionValueDiff($old, $new),
       self::getTransactionValueDiff($new, $old),
     );
   }
 
   private static function getTransactionValueDiff(array $u, array $v) {
     $set = self::getSetFromTransactionValue($v);
 
     foreach ($u as $key => $ref) {
       if (self::isRefInSet($ref, $set)) {
         unset($u[$key]);
       }
     }
 
     return $u;
   }
 
   public static function getSetFromTransactionValue(array $v) {
     $set = array();
     foreach ($v as $ref) {
       $set[$ref['repositoryPHID']][$ref['path']][$ref['excluded']] = true;
     }
     return $set;
   }
 
   public static function isRefInSet(array $ref, array $set) {
     return isset($set[$ref['repositoryPHID']][$ref['path']][$ref['excluded']]);
   }
 
   /**
    * Get the number of directory matches between this path specification and
    * some real path.
    */
   public function getPathMatchStrength($path_fragments, $path_count) {
     $this_path = $this->path;
 
     if ($this_path === '/') {
       // The root path "/" just matches everything with strength 1.
       return 1;
     }
 
     if ($this->fragments === null) {
       $this->fragments = PhabricatorOwnersPackage::splitPath($this_path);
       $this->fragmentCount = count($this->fragments);
     }
 
     $self_fragments = $this->fragments;
     $self_count = $this->fragmentCount;
     if ($self_count > $path_count) {
       // If this path is longer (and therefore more specific) than the target
       // path, we don't match it at all.
       return 0;
     }
 
     for ($ii = 0; $ii < $self_count; $ii++) {
       if ($self_fragments[$ii] != $path_fragments[$ii]) {
         return 0;
       }
     }
 
     return $self_count;
   }
 
 }