diff --git a/lib/legacy/legacy-data-mixin.js b/lib/legacy/legacy-data-mixin.js
index 4401f9539c..cc9aa2b55b 100644
--- a/lib/legacy/legacy-data-mixin.js
+++ b/lib/legacy/legacy-data-mixin.js
@@ -35,15 +35,20 @@ const UndefinedArgumentError = class extends Error {
  * 2.x+ by allowing legacy code to work while identifying observers and
  * computing functions that need undefined checks to work without
  * the mixin in Polymer 2.
+ *
+ * @mixinFunction
+ * @polymer
+ * @summary Mixin to selectively add back Polymer 1.x's `undefined` rules
+ * governing when observers & computing functions run.
  */
 export const LegacyDataMixin = dedupingMixin(superClass => {
 
   /**
-   * @polymer
-   * @mixinClass
-   * @implements {Polymer_LegacyDataMixin}
-   */
-  class LegacyDataMixinClass extends superClass {
+   * @constructor
+   * @extends {superClass}
+   * @unrestricted
+   * @private   */
+  class LegacyDataMixin extends superClass {
     /**
      * Overrides `Polyer.PropertyEffects` to add `undefined` argument
      * checking to match Polymer 1.x style rules
@@ -98,7 +103,7 @@ export const LegacyDataMixin = dedupingMixin(superClass => {
 
   }
 
-  return LegacyDataMixinClass;
+  return LegacyDataMixin;
 
 });