diff --git a/js/lib/dom.js b/js/lib/dom.js
index 00051e0..81c5af7 100644
--- a/js/lib/dom.js
+++ b/js/lib/dom.js
@@ -1,7 +1,9 @@
 let range = null;
 
 export function parseHTML(html) {
-  if (range == null) { range = document.createRange() }
+  if (! (range instanceof Range)) {
+    range = document.createRange();
+  }
   return range.createContextualFragment(html);
 }