diff --git a/resources/sql/autopatches/20181031.board.01.queryreset.php b/resources/sql/autopatches/20181031.board.01.queryreset.php
new file mode 100644
--- /dev/null
+++ b/resources/sql/autopatches/20181031.board.01.queryreset.php
@@ -0,0 +1,50 @@
+<?php
+
+// See T13208. It was previously possible to replace a saved query with another
+// saved query, causing loss of the first query. Find projects which have their
+// default query set to an invalid query and throw the setting away.
+
+$viewer = PhabricatorUser::getOmnipotentUser();
+
+$table = new PhabricatorProject();
+$conn = $table->establishConnection('w');
+
+$iterator = new LiskMigrationIterator($table);
+$search_engine = id(new ManiphestTaskSearchEngine())
+  ->setViewer($viewer);
+
+foreach ($iterator as $project) {
+  $default_filter = $project->getDefaultWorkboardFilter();
+  if (!strlen($default_filter)) {
+    continue;
+  }
+
+  if ($search_engine->isBuiltinQuery($default_filter)) {
+    continue;
+  }
+
+  $saved = id(new PhabricatorSavedQueryQuery())
+    ->setViewer($viewer)
+    ->withQueryKeys(array($default_filter))
+    ->executeOne();
+  if ($saved) {
+    continue;
+  }
+
+  $properties = $project->getProperties();
+  unset($properties['workboard.filter.default']);
+
+  queryfx(
+    $conn,
+    'UPDATE %T SET properties = %s WHERE id = %d',
+    $table->getTableName(),
+    phutil_json_encode($properties),
+    $project->getID());
+
+  echo tsprintf(
+    "%s\n",
+    pht(
+      'Project ("%s") had an invalid query saved as a default workboard '.
+      'query. The query has been reset. See T13208.',
+      $project->getDisplayName()));
+}
diff --git a/src/applications/project/controller/PhabricatorProjectBoardViewController.php b/src/applications/project/controller/PhabricatorProjectBoardViewController.php
--- a/src/applications/project/controller/PhabricatorProjectBoardViewController.php
+++ b/src/applications/project/controller/PhabricatorProjectBoardViewController.php
@@ -203,7 +203,7 @@
       // with the column filter. If the user currently has constraints on the
       // board, we want to add a new column or project constraint, not
       // completely replace the constraints.
-      $saved_query = clone $saved;
+      $saved_query = $saved->newCopy();
 
       if ($query_column->getProxyPHID()) {
         $project_phids = $saved_query->getParameter('projectPHIDs');
diff --git a/src/applications/search/engine/PhabricatorApplicationSearchEngine.php b/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
--- a/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
+++ b/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
@@ -103,6 +103,14 @@
   }
 
   public function saveQuery(PhabricatorSavedQuery $query) {
+    if ($query->getID()) {
+      throw new Exception(
+        pht(
+          'Query (with ID "%s") has already been saved. Queries are '.
+          'immutable once saved.',
+          $query->getID()));
+    }
+
     $query->setEngineClassName(get_class($this));
 
     $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
diff --git a/src/applications/search/storage/PhabricatorSavedQuery.php b/src/applications/search/storage/PhabricatorSavedQuery.php
--- a/src/applications/search/storage/PhabricatorSavedQuery.php
+++ b/src/applications/search/storage/PhabricatorSavedQuery.php
@@ -63,6 +63,13 @@
     return $this->assertAttachedKey($this->parameterMap, $key);
   }
 
+  public function newCopy() {
+    return id(new self())
+      ->setParameters($this->getParameters())
+      ->setQueryKey(null)
+      ->setEngineClassName($this->getEngineClassName());
+  }
+
 
 /* -(  PhabricatorPolicyInterface  )----------------------------------------- */