diff --git a/src/adapt/toc.js b/src/adapt/toc.js
index <HASH>..<HASH> 100644
--- a/src/adapt/toc.js
+++ b/src/adapt/toc.js
@@ -152,7 +152,7 @@ adapt.toc.TOCView.prototype.makeCustomRenderer = function(xmldoc) {
 };
 
 /**
- * @param {HTMLElement} elem
+ * @param {!HTMLElement} elem
  * @param {adapt.vgen.Viewport} viewport
  * @param {number} width
  * @param {number} height
diff --git a/src/adapt/vtree.js b/src/adapt/vtree.js
index <HASH>..<HASH> 100644
--- a/src/adapt/vtree.js
+++ b/src/adapt/vtree.js
@@ -80,7 +80,7 @@ adapt.vtree.makeListener = function(refs, action) {
 };
 
 /**
- * @param {HTMLElement} container
+ * @param {!HTMLElement} container
  * @constructor
  * @extends {adapt.base.SimpleEventTarget}
  */
Refine type annotation (add non-null constraint)