diff --git a/src/core/hiwire.c b/src/core/hiwire.c
index 0756fc400..7808fcd25 100644
--- a/src/core/hiwire.c
+++ b/src/core/hiwire.c
@@ -604,7 +604,10 @@ EM_JS_NUM(bool, hiwire_is_comlink_proxy, (JsRef idobj), {
 EM_JS_NUM(bool, hiwire_is_error, (JsRef idobj), {
   // From https://stackoverflow.com/a/45496068
   let value = Module.hiwire.get_value(idobj);
-  return !!(value && value.stack && value.message);
+  // clang-format off
+  return !!(value && typeof value.stack === "string" &&
+            typeof value.message === "string");
+  // clang-format on
 });
 
 EM_JS_NUM(bool, hiwire_is_promise, (JsRef idobj), {