diff --git a/lib/core/utils/flattened-tree.js b/lib/core/utils/flattened-tree.js
index cc324c77c3..e07a6b7a5b 100644
--- a/lib/core/utils/flattened-tree.js
+++ b/lib/core/utils/flattened-tree.js
@@ -108,7 +108,10 @@ function flattenTree(node, shadowId) {
 		retVal.children = realArray.reduce(reduceShadowDOM, []);
 		return [retVal];
 	} else {
-		if (nodeName === 'content') {
+		if (
+			nodeName === 'content' &&
+			typeof node.getDistributedNodes === 'function'
+		) {
 			realArray = Array.from(node.getDistributedNodes());
 			return realArray.reduce(reduceShadowDOM, []);
 		} else if (