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
@@ -623,6 +623,7 @@
     'DiffusionCommitDiffContentHeraldField' => 'applications/diffusion/herald/DiffusionCommitDiffContentHeraldField.php',
     'DiffusionCommitDiffContentRemovedHeraldField' => 'applications/diffusion/herald/DiffusionCommitDiffContentRemovedHeraldField.php',
     'DiffusionCommitDiffEnormousHeraldField' => 'applications/diffusion/herald/DiffusionCommitDiffEnormousHeraldField.php',
+    'DiffusionCommitEditConduitAPIMethod' => 'applications/diffusion/conduit/DiffusionCommitEditConduitAPIMethod.php',
     'DiffusionCommitEditController' => 'applications/diffusion/controller/DiffusionCommitEditController.php',
     'DiffusionCommitEditEngine' => 'applications/diffusion/editor/DiffusionCommitEditEngine.php',
     'DiffusionCommitFulltextEngine' => 'applications/repository/search/DiffusionCommitFulltextEngine.php',
@@ -5316,6 +5317,7 @@
     'DiffusionCommitDiffContentHeraldField' => 'DiffusionCommitHeraldField',
     'DiffusionCommitDiffContentRemovedHeraldField' => 'DiffusionCommitHeraldField',
     'DiffusionCommitDiffEnormousHeraldField' => 'DiffusionCommitHeraldField',
+    'DiffusionCommitEditConduitAPIMethod' => 'PhabricatorEditEngineAPIMethod',
     'DiffusionCommitEditController' => 'DiffusionController',
     'DiffusionCommitEditEngine' => 'PhabricatorEditEngine',
     'DiffusionCommitFulltextEngine' => 'PhabricatorFulltextEngine',
diff --git a/src/applications/diffusion/conduit/DiffusionCommitEditConduitAPIMethod.php b/src/applications/diffusion/conduit/DiffusionCommitEditConduitAPIMethod.php
new file mode 100644
--- /dev/null
+++ b/src/applications/diffusion/conduit/DiffusionCommitEditConduitAPIMethod.php
@@ -0,0 +1,20 @@
+<?php
+
+final class DiffusionCommitEditConduitAPIMethod
+  extends PhabricatorEditEngineAPIMethod {
+
+  public function getAPIMethodName() {
+    return 'diffusion.commit.edit';
+  }
+
+  public function newEditEngine() {
+    return new DiffusionCommitEditEngine();
+  }
+
+  public function getMethodSummary() {
+    return pht(
+      'Apply transactions to edit an existing commit. This method can not '.
+      'create new commits.');
+  }
+
+}
diff --git a/src/applications/diffusion/editor/DiffusionCommitEditEngine.php b/src/applications/diffusion/editor/DiffusionCommitEditEngine.php
--- a/src/applications/diffusion/editor/DiffusionCommitEditEngine.php
+++ b/src/applications/diffusion/editor/DiffusionCommitEditEngine.php
@@ -26,7 +26,16 @@
   }
 
   protected function newEditableObject() {
-    throw new PhutilMethodNotImplementedException();
+    // NOTE: We must return a valid object here so that things like Conduit
+    // documentation generation work. You can't actually create commits via
+    // EditEngine. This is enforced with a "No One" creation policy.
+
+    $repository = new PhabricatorRepository();
+    $data = new PhabricatorRepositoryCommitData();
+
+    return id(new PhabricatorRepositoryCommit())
+      ->attachRepository($repository)
+      ->attachCommitData($data);
   }
 
   protected function newObjectQuery() {