diff --git a/packages/core/evaluate.mjs b/packages/core/evaluate.mjs
index af02a9a9..e2a4585f 100644
--- a/packages/core/evaluate.mjs
+++ b/packages/core/evaluate.mjs
@@ -40,7 +40,9 @@ function safeEval(str, options = {}) {
 export const evaluate = async (code, transpiler, transpilerOptions) => {
   let meta = {};
   //post to iframe parent (like Udels) if it exists...
-  window.parent?.postMessage(code);
+  if (typeof window !== 'undefined') {
+    window.parent?.postMessage(code);
+  }
   if (transpiler) {
     // transform syntactically correct js code to semantically usable code
     const transpiled = transpiler(code, transpilerOptions);