From 3ed6951f2e19c9c548f336e5fb55d1bc2a0fddd1 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 7 Apr 2017 10:29:29 +0530
Subject: [PATCH] Freeze epubReadingSystem

---
 src/pyj/read_book/iframe.pyj | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/pyj/read_book/iframe.pyj b/src/pyj/read_book/iframe.pyj
index 446ef5f0da..1757901286 100644
--- a/src/pyj/read_book/iframe.pyj
+++ b/src/pyj/read_book/iframe.pyj
@@ -59,7 +59,7 @@ class EPUBReadingSystem:
 class IframeBoss:
 
     def __init__(self):
-        window.navigator.epubReadingSystem = EPUBReadingSystem()
+        window.navigator.epubReadingSystem = Object.freeze(EPUBReadingSystem())
         self.ready_sent = False
         self.last_cfi = None
         self.replace_history_on_next_cfi_update = True