diff --git a/test/unit/property-effects-template.html b/test/unit/property-effects-template.html
index 72766e612c..8e55f9bced 100644
--- a/test/unit/property-effects-template.html
+++ b/test/unit/property-effects-template.html
@@ -741,7 +741,9 @@
   const spans = new Set();
   const accumulatedContent = () => {
     Array.from(el.shadowRoot.querySelectorAll('span')).forEach(s => spans.add(s));
-    return Array.from(spans).map(e => e.textContent);
+    const content = [];
+    spans.forEach(e => content.push(e.textContent));
+    return content;
   };
 
   setup(() => {