diff --git a/src/core/pdf_manager.js b/src/core/pdf_manager.js
index d57f4bc3e5f8b..aee66820ab15d 100644
--- a/src/core/pdf_manager.js
+++ b/src/core/pdf_manager.js
@@ -49,7 +49,7 @@ class BasePdfManager {
     // the worker-thread code.
     args.evaluatorOptions.isOffscreenCanvasSupported &&=
       FeatureTest.isOffscreenCanvasSupported;
-    this.evaluatorOptions = args.evaluatorOptions;
+    this.evaluatorOptions = Object.freeze(args.evaluatorOptions);
   }
 
   get docId() {