diff --git a/src/core/worker.js b/src/core/worker.js
index 25dd08ee0..eb51bacfa 100644
--- a/src/core/worker.js
+++ b/src/core/worker.js
@@ -123,20 +123,19 @@ class WorkerMessageHandler {
     if (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
       // Fail early, and predictably, rather than having (some) fonts fail to
       // load/render with slightly cryptic error messages in environments where
-      // the `Array.prototype` has been *incorrectly* extended.
+      // the `{Object, Array}.prototype` has been *incorrectly* extended.
       //
       // PLEASE NOTE: We do *not* want to slow down font parsing by adding
       //              `hasOwnProperty` checks all over the code-base.
-      const enumerableProperties = [];
-      for (const property in []) {
-        enumerableProperties.push(property);
+      const buildMsg = (type, prop) =>
+        `The \`${type}.prototype\` contains unexpected enumerable property ` +
+        `"${prop}", thus breaking e.g. \`for...in\` iteration of ${type}s.`;
+
+      for (const prop in {}) {
+        throw new Error(buildMsg("Object", prop));
       }
-      if (enumerableProperties.length) {
-        throw new Error(
-          "The `Array.prototype` contains unexpected enumerable properties: " +
-            enumerableProperties.join(", ") +
-            "; thus breaking e.g. `for...in` iteration of `Array`s."
-        );
+      for (const prop in []) {
+        throw new Error(buildMsg("Array", prop));
       }
     }
     const workerHandlerName = docId + "_worker";