diff --git a/src/applications/maniphest/editor/ManiphestEditEngine.php b/src/applications/maniphest/editor/ManiphestEditEngine.php
--- a/src/applications/maniphest/editor/ManiphestEditEngine.php
+++ b/src/applications/maniphest/editor/ManiphestEditEngine.php
@@ -465,5 +465,20 @@
     return $map;
   }
 
+  protected function willConfigureFields($object, array $fields) {
+    $subtype = $this->getEditEngineConfiguration()->getSubType();
+    if ($subtype) {
+      foreach ($fields as $key => $field) {
+        if ($field instanceof PhabricatorCustomFieldEditField) {
+          $subtypes = $field->getCustomField()->getFieldConfigValue('subtypes');
+          if ($subtypes && !in_array($subtype, $subtypes)) {
+            unset($fields[$key]);
+          }
+        }
+      }
+    }
+
+    return $fields;
+  }
 
 }
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
@@ -2120,6 +2120,18 @@
           $object,
           $xactions,
           $type);
+
+        /* XXX: This is nasty. We can't otherwise validate that a given field
+         *      is appropriate for the subtype, because we don't have access
+         *      to the EditEngine's configuration, if it even has one.
+         *      Ideally we should do this in two passes, where we sweep all
+         *      the transactions looking for a subtype, set it on the
+         *      TransactionEditor, and can then access that from validation. */
+        if ($this->getIsNewObject() && !empty($xactions)) {
+          foreach ($xactions as $xaction) {
+            $object->setEditEngineSubtype($xaction->getNewValue());
+          }
+        }
         break;
       case PhabricatorTransactions::TYPE_CUSTOMFIELD:
         $groups = array();
diff --git a/src/infrastructure/customfield/standard/PhabricatorStandardCustomField.php b/src/infrastructure/customfield/standard/PhabricatorStandardCustomField.php
--- a/src/infrastructure/customfield/standard/PhabricatorStandardCustomField.php
+++ b/src/infrastructure/customfield/standard/PhabricatorStandardCustomField.php
@@ -345,6 +345,17 @@
       $type,
       $xactions);
 
+    $object = $this->getObject();
+    if ($object instanceof PhabricatorEditEngineSubtypeInterface) {
+      $subtype = $object->getEditEngineSubtype();
+      if ($subtype) {
+        $subtypes = $this->getFieldConfigValue('subtypes');
+        if ($subtypes && !in_array($subtype, $subtypes)) {
+          return $errors;
+        }
+      }
+    }
+
     if ($this->getRequired()) {
       $value = $this->getOldValueForApplicationTransactions();