diff --git a/src/applications/differential/customfield/DifferentialCoreCustomField.php b/src/applications/differential/customfield/DifferentialCoreCustomField.php
index 6d956ac367..f88ac8836c 100644
--- a/src/applications/differential/customfield/DifferentialCoreCustomField.php
+++ b/src/applications/differential/customfield/DifferentialCoreCustomField.php
@@ -1,163 +1,122 @@
 <?php
 
 /**
  * Base class for Differential fields with storage on the revision object
  * itself. This mostly wraps reading/writing field values to and from the
  * object.
  */
 abstract class DifferentialCoreCustomField
   extends DifferentialCustomField {
 
   private $value;
   private $fieldError;
   private $fieldParser;
 
   abstract protected function readValueFromRevision(
     DifferentialRevision $revision);
 
   protected function writeValueToRevision(
     DifferentialRevision $revision,
     $value) {
     throw new PhabricatorCustomFieldImplementationIncompleteException($this);
   }
 
   protected function isCoreFieldRequired() {
     return false;
   }
 
   protected function isCoreFieldValueEmpty($value) {
     if (is_array($value)) {
       return !$value;
     }
     return !strlen(trim($value));
   }
 
   protected function getCoreFieldRequiredErrorString() {
     throw new PhabricatorCustomFieldImplementationIncompleteException($this);
   }
 
   public function validateApplicationTransactions(
     PhabricatorApplicationTransactionEditor $editor,
     $type,
     array $xactions) {
 
     $this->setFieldError(null);
 
     $errors = parent::validateApplicationTransactions(
       $editor,
       $type,
       $xactions);
 
     $transaction = null;
     foreach ($xactions as $xaction) {
       $value = $xaction->getNewValue();
       if ($this->isCoreFieldRequired()) {
         if ($this->isCoreFieldValueEmpty($value)) {
           $error = new PhabricatorApplicationTransactionValidationError(
             $type,
             pht('Required'),
             $this->getCoreFieldRequiredErrorString(),
             $xaction);
           $error->setIsMissingFieldError(true);
           $errors[] = $error;
           $this->setFieldError(pht('Required'));
           continue;
         }
       }
-
-      if (is_string($value)) {
-        $parser = $this->getFieldParser();
-        $result = $parser->parseCorpus($value);
-
-        unset($result['__title__']);
-        unset($result['__summary__']);
-
-        if ($result) {
-          $error = new PhabricatorApplicationTransactionValidationError(
-            $type,
-            pht('Invalid'),
-            pht(
-              'The value you have entered in "%s" can not be parsed '.
-              'unambiguously when rendered in a commit message. Edit the '.
-              'message so that keywords like "Summary:" and "Test Plan:" do '.
-              'not appear at the beginning of lines. Parsed keys: %s.',
-              $this->getFieldName(),
-              implode(', ', array_keys($result))),
-            $xaction);
-          $errors[] = $error;
-          $this->setFieldError(pht('Invalid'));
-          continue;
-        }
-      }
     }
 
     return $errors;
   }
 
-  private function getFieldParser() {
-    if (!$this->fieldParser) {
-      $viewer = $this->getViewer();
-      $parser = DifferentialCommitMessageParser::newStandardParser($viewer);
-
-      // Set custom title and summary keys so we can detect the presence of
-      // "Summary:" in, e.g., a test plan.
-      $parser->setTitleKey('__title__');
-      $parser->setSummaryKey('__summary__');
-
-      $this->fieldParser = $parser;
-    }
-
-    return $this->fieldParser;
-  }
-
   public function canDisableField() {
     return false;
   }
 
   public function shouldAppearInApplicationTransactions() {
     return true;
   }
 
   public function readValueFromObject(PhabricatorCustomFieldInterface $object) {
     if ($this->isCoreFieldRequired()) {
       $this->setFieldError(true);
     }
     $this->setValue($this->readValueFromRevision($object));
   }
 
   public function getOldValueForApplicationTransactions() {
     return $this->readValueFromRevision($this->getObject());
   }
 
   public function getNewValueForApplicationTransactions() {
     return $this->getValue();
   }
 
   public function applyApplicationTransactionInternalEffects(
     PhabricatorApplicationTransaction $xaction) {
     $this->writeValueToRevision($this->getObject(), $xaction->getNewValue());
   }
 
   public function setFieldError($field_error) {
     $this->fieldError = $field_error;
     return $this;
   }
 
   public function getFieldError() {
     return $this->fieldError;
   }
 
   public function setValue($value) {
     $this->value = $value;
     return $this;
   }
 
   public function getValue() {
     return $this->value;
   }
 
   public function getConduitDictionaryValue() {
     return $this->getValue();
   }
 
 }
diff --git a/src/applications/differential/field/DifferentialTestPlanCommitMessageField.php b/src/applications/differential/field/DifferentialTestPlanCommitMessageField.php
index a477a9036e..178e51d985 100644
--- a/src/applications/differential/field/DifferentialTestPlanCommitMessageField.php
+++ b/src/applications/differential/field/DifferentialTestPlanCommitMessageField.php
@@ -1,53 +1,60 @@
 <?php
 
 final class DifferentialTestPlanCommitMessageField
   extends DifferentialCommitMessageField {
 
   const FIELDKEY = 'testPlan';
 
   public function getFieldName() {
     return pht('Test Plan');
   }
 
   public function getFieldOrder() {
     return 3000;
   }
 
   public function getFieldAliases() {
     return array(
       'Testplan',
       'Tested',
       'Tests',
     );
   }
 
   public function isFieldEnabled() {
     return $this->isCustomFieldEnabled('differential:test-plan');
   }
 
   public function validateFieldValue($value) {
     $is_required = PhabricatorEnv::getEnvConfig(
       'differential.require-test-plan-field');
 
     if ($is_required && !strlen($value)) {
       $this->raiseValidationException(
         pht(
           'You must provide a test plan. Describe the actions you performed '.
           'to verify the behavior of this change.'));
     }
   }
 
   public function readFieldValueFromObject(DifferentialRevision $revision) {
     return $revision->getTestPlan();
   }
 
   public function getFieldTransactions($value) {
     return array(
       array(
         'type' => DifferentialRevisionTestPlanTransaction::EDITKEY,
         'value' => $value,
       ),
     );
   }
 
+  public function validateTransactions($object, array $xactions) {
+    return $this->validateCommitMessageCorpusTransactions(
+      $object,
+      $xactions,
+      pht('Test Plan'));
+  }
+
 }
diff --git a/src/applications/differential/xaction/DifferentialRevisionSummaryTransaction.php b/src/applications/differential/xaction/DifferentialRevisionSummaryTransaction.php
index a4f1dcafa5..238eb53903 100644
--- a/src/applications/differential/xaction/DifferentialRevisionSummaryTransaction.php
+++ b/src/applications/differential/xaction/DifferentialRevisionSummaryTransaction.php
@@ -1,57 +1,64 @@
 <?php
 
 final class DifferentialRevisionSummaryTransaction
   extends DifferentialRevisionTransactionType {
 
   const TRANSACTIONTYPE = 'differential.revision.summary';
   const EDITKEY = 'summary';
 
   public function generateOldValue($object) {
     return $object->getSummary();
   }
 
   public function applyInternalEffects($object, $value) {
     $object->setSummary($value);
   }
 
   public function getTitle() {
     return pht(
       '%s edited the summary of this revision.',
       $this->renderAuthor());
   }
 
   public function getTitleForFeed() {
     return pht(
       '%s updated the summary of %s.',
       $this->renderAuthor(),
       $this->renderObject());
   }
 
   public function hasChangeDetailView() {
     return true;
   }
 
   public function getMailDiffSectionHeader() {
     return pht('CHANGES TO REVISION SUMMARY');
   }
 
   public function newChangeDetailView() {
     $viewer = $this->getViewer();
 
     return id(new PhabricatorApplicationTransactionTextDiffDetailView())
       ->setViewer($viewer)
       ->setOldText($this->getOldValue())
       ->setNewText($this->getNewValue());
   }
 
   public function newRemarkupChanges() {
     $changes = array();
 
     $changes[] = $this->newRemarkupChange()
       ->setOldValue($this->getOldValue())
       ->setNewValue($this->getNewValue());
 
     return $changes;
   }
 
+  public function validateTransactions($object, array $xactions) {
+    return $this->validateCommitMessageCorpusTransactions(
+      $object,
+      $xactions,
+      pht('Summary'));
+  }
+
 }
diff --git a/src/applications/differential/xaction/DifferentialRevisionTransactionType.php b/src/applications/differential/xaction/DifferentialRevisionTransactionType.php
index f740d97c74..59b0c7510d 100644
--- a/src/applications/differential/xaction/DifferentialRevisionTransactionType.php
+++ b/src/applications/differential/xaction/DifferentialRevisionTransactionType.php
@@ -1,4 +1,60 @@
 <?php
 
 abstract class DifferentialRevisionTransactionType
-  extends PhabricatorModularTransactionType {}
+  extends PhabricatorModularTransactionType {
+
+  protected function validateCommitMessageCorpusTransactions(
+    $object,
+    array $xactions,
+    $field_name) {
+
+    $errors = array();
+    foreach ($xactions as $xaction) {
+      $error = $this->validateMessageCorpus($xaction, $field_name);
+      if ($error) {
+        $errors[] = $error;
+      }
+    }
+
+    return $errors;
+  }
+
+  private function validateMessageCorpus($xaction, $field_name) {
+    $value = $xaction->getNewValue();
+    if (!strlen($value)) {
+      return null;
+    }
+
+    // Put a placeholder title on the message, because the first line of a
+    // message is now always parsed as a title.
+    $value = "<placeholder>\n".$value;
+
+    $viewer = $this->getActor();
+    $parser = DifferentialCommitMessageParser::newStandardParser($viewer);
+
+    // Set custom title and summary keys so we can detect the presence of
+    // "Summary:" in, e.g., a test plan.
+    $parser->setTitleKey('__title__');
+    $parser->setSummaryKey('__summary__');
+
+    $result = $parser->parseCorpus($value);
+
+    unset($result['__title__']);
+    unset($result['__summary__']);
+
+    if (!$result) {
+      return null;
+    }
+
+    return $this->newInvalidError(
+      pht(
+        'The value you have entered in "%s" can not be parsed '.
+        'unambiguously when rendered in a commit message. Edit the '.
+        'message so that keywords like "Summary:" and "Test Plan:" do '.
+        'not appear at the beginning of lines. Parsed keys: %s.',
+        $field_name,
+        implode(', ', array_keys($result))),
+      $xaction);
+  }
+
+}