diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -2976,6 +2976,7 @@
     'PhabricatorEditEngineStaticCommentAction' => 'applications/transactions/commentaction/PhabricatorEditEngineStaticCommentAction.php',
     'PhabricatorEditEngineSubtype' => 'applications/transactions/editengine/PhabricatorEditEngineSubtype.php',
     'PhabricatorEditEngineSubtypeInterface' => 'applications/transactions/editengine/PhabricatorEditEngineSubtypeInterface.php',
+    'PhabricatorEditEngineSubtypeMap' => 'applications/transactions/editengine/PhabricatorEditEngineSubtypeMap.php',
     'PhabricatorEditEngineSubtypeTestCase' => 'applications/transactions/editengine/__tests__/PhabricatorEditEngineSubtypeTestCase.php',
     'PhabricatorEditEngineTokenizerCommentAction' => 'applications/transactions/commentaction/PhabricatorEditEngineTokenizerCommentAction.php',
     'PhabricatorEditField' => 'applications/transactions/editfield/PhabricatorEditField.php',
@@ -8729,6 +8730,7 @@
     'PhabricatorEditEngineSettingsPanel' => 'PhabricatorSettingsPanel',
     'PhabricatorEditEngineStaticCommentAction' => 'PhabricatorEditEngineCommentAction',
     'PhabricatorEditEngineSubtype' => 'Phobject',
+    'PhabricatorEditEngineSubtypeMap' => 'Phobject',
     'PhabricatorEditEngineSubtypeTestCase' => 'PhabricatorTestCase',
     'PhabricatorEditEngineTokenizerCommentAction' => 'PhabricatorEditEngineCommentAction',
     'PhabricatorEditField' => 'Phobject',
diff --git a/src/applications/maniphest/query/ManiphestTaskSearchEngine.php b/src/applications/maniphest/query/ManiphestTaskSearchEngine.php
--- a/src/applications/maniphest/query/ManiphestTaskSearchEngine.php
+++ b/src/applications/maniphest/query/ManiphestTaskSearchEngine.php
@@ -47,7 +47,7 @@
     // Hide the "Subtypes" constraint from the web UI if the install only
     // defines one task subtype, since it isn't of any use in this case.
     $subtype_map = id(new ManiphestTask())->newEditEngineSubtypeMap();
-    $hide_subtypes = (count($subtype_map) == 1);
+    $hide_subtypes = ($subtype_map->getCount() == 1);
 
     return array(
       id(new PhabricatorOwnersSearchField())
diff --git a/src/applications/maniphest/storage/ManiphestTask.php b/src/applications/maniphest/storage/ManiphestTask.php
--- a/src/applications/maniphest/storage/ManiphestTask.php
+++ b/src/applications/maniphest/storage/ManiphestTask.php
@@ -573,7 +573,7 @@
   public function newSubtypeObject() {
     $subtype_key = $this->getEditEngineSubtype();
     $subtype_map = $this->newEditEngineSubtypeMap();
-    return idx($subtype_map, $subtype_key);
+    return $subtype_map->getSubtype($subtype_key);
   }
 
 /* -(  PhabricatorFulltextInterface  )--------------------------------------- */
diff --git a/src/applications/maniphest/storage/ManiphestTransaction.php b/src/applications/maniphest/storage/ManiphestTransaction.php
--- a/src/applications/maniphest/storage/ManiphestTransaction.php
+++ b/src/applications/maniphest/storage/ManiphestTransaction.php
@@ -214,11 +214,12 @@
   public function renderSubtypeName($value) {
     $object = $this->getObject();
     $map = $object->newEditEngineSubtypeMap();
-    if (!isset($map[$value])) {
+
+    if (!$map->isValidSubtype($value)) {
       return $value;
     }
 
-    return $map[$value]->getName();
+    return $map->getSubtype($value)->getName();
   }
 
 }
diff --git a/src/applications/maniphest/typeahead/ManiphestTaskSubtypeDatasource.php b/src/applications/maniphest/typeahead/ManiphestTaskSubtypeDatasource.php
--- a/src/applications/maniphest/typeahead/ManiphestTaskSubtypeDatasource.php
+++ b/src/applications/maniphest/typeahead/ManiphestTaskSubtypeDatasource.php
@@ -28,7 +28,7 @@
     $results = array();
 
     $subtype_map = id(new ManiphestTask())->newEditEngineSubtypeMap();
-    foreach ($subtype_map as $key => $subtype) {
+    foreach ($subtype_map->getSubtypes() as $key => $subtype) {
 
       $result = id(new PhabricatorTypeaheadResult())
         ->setIcon($subtype->getIcon())
diff --git a/src/applications/maniphest/view/ManiphestTaskListView.php b/src/applications/maniphest/view/ManiphestTaskListView.php
--- a/src/applications/maniphest/view/ManiphestTaskListView.php
+++ b/src/applications/maniphest/view/ManiphestTaskListView.php
@@ -56,9 +56,6 @@
       Javelin::initBehavior('maniphest-list-editor');
     }
 
-    $subtype_map = id(new ManiphestTask())
-      ->newEditEngineSubtypeMap();
-
     foreach ($this->tasks as $task) {
       $item = id(new PHUIObjectItemView())
         ->setUser($this->getUser())
diff --git a/src/applications/transactions/controller/PhabricatorEditEngineConfigurationSubtypeController.php b/src/applications/transactions/controller/PhabricatorEditEngineConfigurationSubtypeController.php
--- a/src/applications/transactions/controller/PhabricatorEditEngineConfigurationSubtypeController.php
+++ b/src/applications/transactions/controller/PhabricatorEditEngineConfigurationSubtypeController.php
@@ -61,8 +61,7 @@
 EOTEXT
       );
 
-    $map = $engine->newSubtypeMap();
-    $map = mpull($map, 'getName');
+    $map = $engine->newSubtypeMap()->getDisplayMap();
 
     $form = id(new AphrontFormView())
       ->setUser($viewer)
diff --git a/src/applications/transactions/editengine/PhabricatorEditEngineSubtype.php b/src/applications/transactions/editengine/PhabricatorEditEngineSubtype.php
--- a/src/applications/transactions/editengine/PhabricatorEditEngineSubtype.php
+++ b/src/applications/transactions/editengine/PhabricatorEditEngineSubtype.php
@@ -182,7 +182,7 @@
       $map[$key] = $subtype;
     }
 
-    return $map;
+    return new PhabricatorEditEngineSubtypeMap($map);
   }
 
 }
diff --git a/src/applications/transactions/editengine/PhabricatorEditEngineSubtypeMap.php b/src/applications/transactions/editengine/PhabricatorEditEngineSubtypeMap.php
new file mode 100644
--- /dev/null
+++ b/src/applications/transactions/editengine/PhabricatorEditEngineSubtypeMap.php
@@ -0,0 +1,42 @@
+<?php
+
+
+final class PhabricatorEditEngineSubtypeMap
+  extends Phobject {
+
+  private $subtypes;
+
+  public function __construct(array $subtypes) {
+    assert_instances_of($subtypes, 'PhabricatorEditEngineSubtype');
+
+    $this->subtypes = $subtypes;
+  }
+
+  public function getDisplayMap() {
+    return mpull($this->subtypes, 'getName');
+  }
+
+  public function getCount() {
+    return count($this->subtypes);
+  }
+
+  public function isValidSubtype($subtype_key) {
+    return isset($this->subtypes[$subtype_key]);
+  }
+
+  public function getSubtypes() {
+    return $this->subtypes;
+  }
+
+  public function getSubtype($subtype_key) {
+    if (!$this->isValidSubtype($subtype_key)) {
+      throw new Exception(
+        pht(
+          'Subtype key "%s" does not identify a valid subtype.',
+          $subtype_key));
+    }
+
+    return $this->subtypes[$subtype_key];
+  }
+
+}
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
@@ -2541,7 +2541,7 @@
         continue;
       }
 
-      if (!isset($map[$new])) {
+      if (!$map->isValidSubtype($new)) {
         $errors[] = new PhabricatorApplicationTransactionValidationError(
           $transaction_type,
           pht('Invalid'),
diff --git a/src/applications/transactions/editor/PhabricatorEditEngineConfigurationEditor.php b/src/applications/transactions/editor/PhabricatorEditEngineConfigurationEditor.php
--- a/src/applications/transactions/editor/PhabricatorEditEngineConfigurationEditor.php
+++ b/src/applications/transactions/editor/PhabricatorEditEngineConfigurationEditor.php
@@ -64,7 +64,7 @@
           foreach ($xactions as $xaction) {
             $new = $xaction->getNewValue();
 
-            if (isset($map[$new])) {
+            if ($map->isValidSubtype($new)) {
               continue;
             }
 
diff --git a/src/applications/transactions/engineextension/PhabricatorSubtypeEditEngineExtension.php b/src/applications/transactions/engineextension/PhabricatorSubtypeEditEngineExtension.php
--- a/src/applications/transactions/engineextension/PhabricatorSubtypeEditEngineExtension.php
+++ b/src/applications/transactions/engineextension/PhabricatorSubtypeEditEngineExtension.php
@@ -31,7 +31,7 @@
     $subtype_type = PhabricatorTransactions::TYPE_SUBTYPE;
 
     $map = $object->newEditEngineSubtypeMap();
-    $options = mpull($map, 'getName');
+    $options = $map->getDisplayMap();
 
     $subtype_field = id(new PhabricatorSelectEditField())
       ->setKey(self::EDITKEY)
@@ -45,7 +45,7 @@
 
     // If subtypes are configured, enable changing them from the bulk editor
     // and comment action stack.
-    if (count($map) > 1) {
+    if ($map->getCount() > 1) {
       $subtype_field
         ->setBulkEditLabel(pht('Change subtype to'))
         ->setCommentActionLabel(pht('Change Subtype'))