diff --git a/src/pyj/book_list/book_details.pyj b/src/pyj/book_list/book_details.pyj
index 25b5b48078..0cdd77fc09 100644
--- a/src/pyj/book_list/book_details.pyj
+++ b/src/pyj/book_list/book_details.pyj
@@ -132,7 +132,7 @@ def adjusting_sandboxed_html(html):
     css =  'html, body {{ overflow: hidden; color: {} }}'.format(get_color('window-foreground'))
     # allow-same-origin is needed for resizing and allow-popups is needed for
     # target="_blank"
-    ans = sandboxed_html(html, css, 'allow-same-origin allow-popups')
+    ans = sandboxed_html(html, css, 'allow-same-origin allow-popups allow-popups-to-escape-sandbox')
     ans.addEventListener('load', def(ev): setup_iframe(ev.target);)
     ans.style.height = '50vh'
     ans.dataset.last_window_width = '0'
diff --git a/src/pyj/read_book/view.pyj b/src/pyj/read_book/view.pyj
index 3cded9fdcf..a24e01a618 100644
--- a/src/pyj/read_book/view.pyj
+++ b/src/pyj/read_book/view.pyj
@@ -135,7 +135,7 @@ class View:
                         left_margin,
                         E.div(style='flex-grow:2; display:flex; align-items:stretch; flex-direction: column', # container for top and bottom margins
                             margin_elem(sd, 'margin_top', 'book-top-margin', self.top_margin_clicked),
-                            E.iframe(id=iframe_id, seamless=True, sandbox='allow-popups allow-scripts', style='flex-grow: 2', allowfullscreen='true'),
+                            E.iframe(id=iframe_id, seamless=True, sandbox='allow-popups allow-scripts allow-popups-to-escape-sandbox', style='flex-grow: 2', allowfullscreen='true'),
                             margin_elem(sd, 'margin_bottom', 'book-bottom-margin'),
                         ),
                         right_margin,