diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index cd50024b6f..4cddbeeb2a 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1475,6 +1475,7 @@ phutil_register_library_map(array(
     'HarbormasterBuildableEngine' => 'applications/harbormaster/engine/HarbormasterBuildableEngine.php',
     'HarbormasterBuildableInterface' => 'applications/harbormaster/interface/HarbormasterBuildableInterface.php',
     'HarbormasterBuildableListController' => 'applications/harbormaster/controller/HarbormasterBuildableListController.php',
+    'HarbormasterBuildableMessageTransaction' => 'applications/harbormaster/xaction/buildable/HarbormasterBuildableMessageTransaction.php',
     'HarbormasterBuildablePHIDType' => 'applications/harbormaster/phid/HarbormasterBuildablePHIDType.php',
     'HarbormasterBuildableQuery' => 'applications/harbormaster/query/HarbormasterBuildableQuery.php',
     'HarbormasterBuildableSearchAPIMethod' => 'applications/harbormaster/conduit/HarbormasterBuildableSearchAPIMethod.php',
@@ -1483,6 +1484,7 @@ phutil_register_library_map(array(
     'HarbormasterBuildableTransaction' => 'applications/harbormaster/storage/HarbormasterBuildableTransaction.php',
     'HarbormasterBuildableTransactionEditor' => 'applications/harbormaster/editor/HarbormasterBuildableTransactionEditor.php',
     'HarbormasterBuildableTransactionQuery' => 'applications/harbormaster/query/HarbormasterBuildableTransactionQuery.php',
+    'HarbormasterBuildableTransactionType' => 'applications/harbormaster/xaction/buildable/HarbormasterBuildableTransactionType.php',
     'HarbormasterBuildableViewController' => 'applications/harbormaster/controller/HarbormasterBuildableViewController.php',
     'HarbormasterBuildkiteBuildStepImplementation' => 'applications/harbormaster/step/HarbormasterBuildkiteBuildStepImplementation.php',
     'HarbormasterBuildkiteBuildableInterface' => 'applications/harbormaster/interface/HarbormasterBuildkiteBuildableInterface.php',
@@ -7730,14 +7732,16 @@ phutil_register_library_map(array(
     'HarbormasterBuildableActionController' => 'HarbormasterController',
     'HarbormasterBuildableEngine' => 'Phobject',
     'HarbormasterBuildableListController' => 'HarbormasterController',
+    'HarbormasterBuildableMessageTransaction' => 'HarbormasterBuildableTransactionType',
     'HarbormasterBuildablePHIDType' => 'PhabricatorPHIDType',
     'HarbormasterBuildableQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
     'HarbormasterBuildableSearchAPIMethod' => 'PhabricatorSearchEngineAPIMethod',
     'HarbormasterBuildableSearchEngine' => 'PhabricatorApplicationSearchEngine',
     'HarbormasterBuildableStatus' => 'Phobject',
-    'HarbormasterBuildableTransaction' => 'PhabricatorApplicationTransaction',
+    'HarbormasterBuildableTransaction' => 'PhabricatorModularTransaction',
     'HarbormasterBuildableTransactionEditor' => 'PhabricatorApplicationTransactionEditor',
     'HarbormasterBuildableTransactionQuery' => 'PhabricatorApplicationTransactionQuery',
+    'HarbormasterBuildableTransactionType' => 'PhabricatorModularTransactionType',
     'HarbormasterBuildableViewController' => 'HarbormasterController',
     'HarbormasterBuildkiteBuildStepImplementation' => 'HarbormasterBuildStepImplementation',
     'HarbormasterBuildkiteHookController' => 'HarbormasterController',
diff --git a/src/applications/harbormaster/controller/HarbormasterBuildableActionController.php b/src/applications/harbormaster/controller/HarbormasterBuildableActionController.php
index cfed19a6c1..b0c74139db 100644
--- a/src/applications/harbormaster/controller/HarbormasterBuildableActionController.php
+++ b/src/applications/harbormaster/controller/HarbormasterBuildableActionController.php
@@ -111,18 +111,14 @@ final class HarbormasterBuildableActionController
         ->setContinueOnNoEffect(true)
         ->setContinueOnMissingFields(true);
 
+      $xaction_type = HarbormasterBuildableMessageTransaction::TRANSACTIONTYPE;
+
       $xaction = id(new HarbormasterBuildableTransaction())
-        ->setTransactionType(HarbormasterBuildableTransaction::TYPE_COMMAND)
+        ->setTransactionType($xaction_type)
         ->setNewValue($action);
 
       $editor->applyTransactions($buildable, array($xaction));
 
-      $build_editor = id(new HarbormasterBuildTransactionEditor())
-        ->setActor($viewer)
-        ->setContentSourceFromRequest($request)
-        ->setContinueOnNoEffect(true)
-        ->setContinueOnMissingFields(true);
-
       foreach ($can_send as $build) {
         $build->sendMessage(
           $viewer,
diff --git a/src/applications/harbormaster/editor/HarbormasterBuildableTransactionEditor.php b/src/applications/harbormaster/editor/HarbormasterBuildableTransactionEditor.php
index 63121813bb..895c89f858 100644
--- a/src/applications/harbormaster/editor/HarbormasterBuildableTransactionEditor.php
+++ b/src/applications/harbormaster/editor/HarbormasterBuildableTransactionEditor.php
@@ -11,60 +11,4 @@ final class HarbormasterBuildableTransactionEditor
     return pht('Harbormaster Buildables');
   }
 
-  public function getTransactionTypes() {
-    $types = parent::getTransactionTypes();
-
-    $types[] = HarbormasterBuildableTransaction::TYPE_COMMAND;
-
-    return $types;
-  }
-
-  protected function getCustomTransactionOldValue(
-    PhabricatorLiskDAO $object,
-    PhabricatorApplicationTransaction $xaction) {
-
-    switch ($xaction->getTransactionType()) {
-      case HarbormasterBuildableTransaction::TYPE_COMMAND:
-        return null;
-    }
-
-    return parent::getCustomTransactionOldValue($object, $xaction);
-  }
-
-  protected function getCustomTransactionNewValue(
-    PhabricatorLiskDAO $object,
-    PhabricatorApplicationTransaction $xaction) {
-
-    switch ($xaction->getTransactionType()) {
-      case HarbormasterBuildableTransaction::TYPE_COMMAND:
-        return $xaction->getNewValue();
-    }
-
-    return parent::getCustomTransactionNewValue($object, $xaction);
-  }
-
-  protected function applyCustomInternalTransaction(
-    PhabricatorLiskDAO $object,
-    PhabricatorApplicationTransaction $xaction) {
-
-    switch ($xaction->getTransactionType()) {
-      case HarbormasterBuildableTransaction::TYPE_COMMAND:
-        return;
-    }
-
-    return parent::applyCustomInternalTransaction($object, $xaction);
-  }
-
-  protected function applyCustomExternalTransaction(
-    PhabricatorLiskDAO $object,
-    PhabricatorApplicationTransaction $xaction) {
-
-    switch ($xaction->getTransactionType()) {
-      case HarbormasterBuildableTransaction::TYPE_COMMAND:
-        return;
-    }
-
-    return parent::applyCustomExternalTransaction($object, $xaction);
-  }
-
 }
diff --git a/src/applications/harbormaster/storage/HarbormasterBuildableTransaction.php b/src/applications/harbormaster/storage/HarbormasterBuildableTransaction.php
index a4a2f1ab14..e3b937df1e 100644
--- a/src/applications/harbormaster/storage/HarbormasterBuildableTransaction.php
+++ b/src/applications/harbormaster/storage/HarbormasterBuildableTransaction.php
@@ -1,9 +1,7 @@
 <?php
 
 final class HarbormasterBuildableTransaction
-  extends PhabricatorApplicationTransaction {
-
-  const TYPE_COMMAND = 'harbormaster:buildable:command';
+  extends PhabricatorModularTransaction {
 
   public function getApplicationName() {
     return 'harbormaster';
@@ -13,72 +11,8 @@ final class HarbormasterBuildableTransaction
     return HarbormasterBuildablePHIDType::TYPECONST;
   }
 
-  public function getTitle() {
-    $author_phid = $this->getAuthorPHID();
-
-    $old = $this->getOldValue();
-    $new = $this->getNewValue();
-
-    switch ($this->getTransactionType()) {
-      case self::TYPE_COMMAND:
-        switch ($new) {
-          case HarbormasterBuildMessageRestartTransaction::MESSAGETYPE:
-            return pht(
-              '%s restarted this buildable.',
-              $this->renderHandleLink($author_phid));
-          case HarbormasterBuildMessageResumeTransaction::MESSAGETYPE:
-            return pht(
-              '%s resumed this buildable.',
-              $this->renderHandleLink($author_phid));
-          case HarbormasterBuildMessagePauseTransaction::MESSAGETYPE:
-            return pht(
-              '%s paused this buildable.',
-              $this->renderHandleLink($author_phid));
-          case HarbormasterBuildMessageAbortTransaction::MESSAGETYPE:
-            return pht(
-              '%s aborted this buildable.',
-              $this->renderHandleLink($author_phid));
-        }
-    }
-    return parent::getTitle();
+  public function getBaseTransactionClass() {
+    return 'HarbormasterBuildableTransactionType';
   }
 
-  public function getIcon() {
-    $author_phid = $this->getAuthorPHID();
-
-    $old = $this->getOldValue();
-    $new = $this->getNewValue();
-
-    switch ($this->getTransactionType()) {
-      case self::TYPE_COMMAND:
-        switch ($new) {
-          case HarbormasterBuildMessageRestartTransaction::MESSAGETYPE:
-            return 'fa-backward';
-          case HarbormasterBuildMessageResumeTransaction::MESSAGETYPE:
-            return 'fa-play';
-          case HarbormasterBuildMessagePauseTransaction::MESSAGETYPE:
-            return 'fa-pause';
-          case HarbormasterBuildMessageAbortTransaction::MESSAGETYPE:
-            return 'fa-exclamation-triangle';
-        }
-    }
-
-    return parent::getIcon();
-  }
-
-  public function getColor() {
-    $author_phid = $this->getAuthorPHID();
-
-    $old = $this->getOldValue();
-    $new = $this->getNewValue();
-
-    switch ($this->getTransactionType()) {
-      case self::TYPE_COMMAND:
-        switch ($new) {
-          case HarbormasterBuildMessagePauseTransaction::MESSAGETYPE:
-            return 'red';
-        }
-    }
-    return parent::getColor();
-  }
 }
diff --git a/src/applications/harbormaster/xaction/buildable/HarbormasterBuildableMessageTransaction.php b/src/applications/harbormaster/xaction/buildable/HarbormasterBuildableMessageTransaction.php
new file mode 100644
index 0000000000..641e9f8bc1
--- /dev/null
+++ b/src/applications/harbormaster/xaction/buildable/HarbormasterBuildableMessageTransaction.php
@@ -0,0 +1,65 @@
+<?php
+
+final class HarbormasterBuildableMessageTransaction
+  extends HarbormasterBuildableTransactionType {
+
+  const TRANSACTIONTYPE = 'harbormaster:buildable:command';
+
+  public function generateOldValue($object) {
+    return null;
+  }
+
+  public function getTitle() {
+    $new = $this->getNewValue();
+
+    switch ($new) {
+      case HarbormasterBuildMessageRestartTransaction::MESSAGETYPE:
+        return pht(
+          '%s restarted this buildable.',
+          $this->renderAuthor());
+      case HarbormasterBuildMessageResumeTransaction::MESSAGETYPE:
+        return pht(
+          '%s resumed this buildable.',
+          $this->renderAuthor());
+      case HarbormasterBuildMessagePauseTransaction::MESSAGETYPE:
+        return pht(
+          '%s paused this buildable.',
+          $this->renderAuthor());
+      case HarbormasterBuildMessageAbortTransaction::MESSAGETYPE:
+        return pht(
+          '%s aborted this buildable.',
+          $this->renderAuthor());
+    }
+
+    return parent::getTitle();
+  }
+
+  public function getIcon() {
+    $new = $this->getNewValue();
+
+    switch ($new) {
+      case HarbormasterBuildMessageRestartTransaction::MESSAGETYPE:
+        return 'fa-backward';
+      case HarbormasterBuildMessageResumeTransaction::MESSAGETYPE:
+        return 'fa-play';
+      case HarbormasterBuildMessagePauseTransaction::MESSAGETYPE:
+        return 'fa-pause';
+      case HarbormasterBuildMessageAbortTransaction::MESSAGETYPE:
+        return 'fa-exclamation-triangle';
+    }
+
+    return parent::getIcon();
+  }
+
+  public function getColor() {
+    $new = $this->getNewValue();
+
+    switch ($new) {
+      case HarbormasterBuildMessagePauseTransaction::MESSAGETYPE:
+        return 'red';
+    }
+
+    return parent::getColor();
+  }
+
+}
diff --git a/src/applications/harbormaster/xaction/buildable/HarbormasterBuildableTransactionType.php b/src/applications/harbormaster/xaction/buildable/HarbormasterBuildableTransactionType.php
new file mode 100644
index 0000000000..0299313104
--- /dev/null
+++ b/src/applications/harbormaster/xaction/buildable/HarbormasterBuildableTransactionType.php
@@ -0,0 +1,4 @@
+<?php
+
+abstract class HarbormasterBuildableTransactionType
+  extends PhabricatorModularTransactionType {}