diff --git a/src/applications/differential/editor/DifferentialDiffEditor.php b/src/applications/differential/editor/DifferentialDiffEditor.php
--- a/src/applications/differential/editor/DifferentialDiffEditor.php
+++ b/src/applications/differential/editor/DifferentialDiffEditor.php
@@ -208,15 +208,6 @@
     return $adapter;
   }
 
-  protected function didApplyHeraldRules(
-    PhabricatorLiskDAO $object,
-    HeraldAdapter $adapter,
-    HeraldTranscript $transcript) {
-
-    $xactions = array();
-    return $xactions;
-  }
-
   private function updateDiffFromDict(DifferentialDiff $diff, $dict) {
     $diff
       ->setSourcePath(idx($dict, 'sourcePath'))
diff --git a/src/applications/herald/adapter/HeraldAdapter.php b/src/applications/herald/adapter/HeraldAdapter.php
--- a/src/applications/herald/adapter/HeraldAdapter.php
+++ b/src/applications/herald/adapter/HeraldAdapter.php
@@ -186,15 +186,16 @@
     return $this->appliedTransactions;
   }
 
-  public function queueTransaction($transaction) {
+  final public function queueTransaction(
+    PhabricatorApplicationTransaction $transaction) {
     $this->queuedTransactions[] = $transaction;
   }
 
-  public function getQueuedTransactions() {
+  final public function getQueuedTransactions() {
     return $this->queuedTransactions;
   }
 
-  public function newTransaction() {
+  final public function newTransaction() {
     $object = $this->newObject();
 
     if (!($object instanceof PhabricatorApplicationTransactionInterface)) {
@@ -205,7 +206,19 @@
           'PhabricatorApplicationTransactionInterface'));
     }
 
-    return $object->getApplicationTransactionTemplate();
+    $xaction = $object->getApplicationTransactionTemplate();
+
+    if (!($xaction instanceof PhabricatorApplicationTransaction)) {
+      throw new Exception(
+        pht(
+          'Expected object (of class "%s") to return a transaction template '.
+          '(of class "%s"), but it returned something else ("%s").',
+          get_class($object),
+          'PhabricatorApplicationTransaction',
+          phutil_describe_type($xaction)));
+    }
+
+    return $xaction;
   }
 
 
diff --git a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
--- a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
+++ b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
@@ -3779,9 +3779,14 @@
 
     $this->mustEncrypt = $adapter->getMustEncryptReasons();
 
+    $apply_xactions = $this->didApplyHeraldRules($object, $adapter, $xscript);
+    assert_instances_of($apply_xactions, 'PhabricatorApplicationTransaction');
+
+    $queue_xactions = $adapter->getQueuedTransactions();
+
     return array_merge(
-      $this->didApplyHeraldRules($object, $adapter, $xscript),
-      $adapter->getQueuedTransactions());
+      array_values($apply_xactions),
+      array_values($queue_xactions));
   }
 
   protected function didApplyHeraldRules(