diff --git a/src/native-tree.ts b/src/native-tree.ts
index d66301d1..190ceb80 100644
--- a/src/native-tree.ts
+++ b/src/native-tree.ts
@@ -365,8 +365,10 @@ export function release(node: NodeMirror): void {
 function subtreeHasRetained(node: NodeMirror): boolean {
   if (!node) return false;
   if (retained.has(node)) return true;
-  for (let i = 0; i < node.children.length; i++) {
-    if (subtreeHasRetained(node.children[i])) return true;
+  if (node.children) {
+    for (let i = 0; i < node.children.length; i++) {
+      if (subtreeHasRetained(node.children[i])) return true;
+    }
   }
   return false;
 }