diff --git a/lib/core/utils/flattened-tree.js b/lib/core/utils/flattened-tree.js
index 5012acb2d3..68dad0f270 100644
--- a/lib/core/utils/flattened-tree.js
+++ b/lib/core/utils/flattened-tree.js
@@ -34,13 +34,13 @@ function virtualDOMfromNode(node, shadowId) {
 		actualNode: node,
 		_isHidden: null, // will be populated by axe.utils.isHidden
 		get isFocusable() {
-			if (!vNodeCache._isFocusable) {
+			if (!vNodeCache.hasOwnProperty('_isFocusable')) {
 				vNodeCache._isFocusable = axe.commons.dom.isFocusable(node);
 			}
 			return vNodeCache._isFocusable;
 		},
 		get tabbableElements() {
-			if (!vNodeCache._tabbableElements) {
+			if (!vNodeCache.hasOwnProperty('_tabbableElements')) {
 				vNodeCache._tabbableElements = axe.commons.dom.getTabbableElements(
 					this
 				);