diff --git a/src/FillSpace.jsx b/src/FillSpace.jsx
index 6cb74fb..ca0d4de 100644
--- a/src/FillSpace.jsx
+++ b/src/FillSpace.jsx
@@ -311,7 +311,7 @@ class FillSpace extends Component {
       containerTarget,
     ];
     for (const el of targets) {
-      if (el && el.offsetParent !== null) {
+      if (el && typeof Element !== 'undefined' && el instanceof Element && el.offsetParent !== null) {
         this.observer.observe(el);
       }
     }