diff --git a/src/calibre/gui2/viewer/web_view.py b/src/calibre/gui2/viewer/web_view.py
index 0dcb91c6f1..a38bf13338 100644
--- a/src/calibre/gui2/viewer/web_view.py
+++ b/src/calibre/gui2/viewer/web_view.py
@@ -9,7 +9,7 @@ import sys
 from itertools import count
 
 from PyQt5.Qt import (
-    QApplication, QBuffer, QByteArray, QFontDatabase, QFontInfo, QHBoxLayout, QSize,
+    QApplication, QBuffer, QByteArray, QFontDatabase, QFontInfo, QHBoxLayout, QSize, QT_VERSION,
     Qt, QTimer, QUrl, QWidget, pyqtSignal
 )
 from PyQt5.QtWebEngineCore import QWebEngineUrlSchemeHandler
@@ -581,6 +581,7 @@ class WebView(RestartingWebEngineView):
             'ui_font_sz': '{}px'.format(fi.pixelSize()),
             'show_home_page_on_ready': self.show_home_page_on_ready,
             'system_colors': system_colors(),
+            'QT_VERSION': QT_VERSION,
         }
         self.bridge.create_view(
             vprefs['session_data'], vprefs['local_storage'], field_metadata.all_metadata(), ui_data)
diff --git a/src/pyj/read_book/globals.pyj b/src/pyj/read_book/globals.pyj
index 3b5175ee56..a5ead3463c 100644
--- a/src/pyj/read_book/globals.pyj
+++ b/src/pyj/read_book/globals.pyj
@@ -81,6 +81,7 @@ runtime = {
     'is_standalone_viewer': False,
     'viewer_in_full_screen': False,
     'in_develop_mode': IN_DEVELOP_MODE is '1',
+    'QT_VERSION': 0,
 }
 
 
diff --git a/src/pyj/viewer-main.pyj b/src/pyj/viewer-main.pyj
index 2393d45aff..3aa54d23cc 100644
--- a/src/pyj/viewer-main.pyj
+++ b/src/pyj/viewer-main.pyj
@@ -175,6 +175,7 @@ def create_view(prefs, local_storage, field_metadata, ui_data):
     library_data.field_metadata = field_metadata
     document.documentElement.style.fontFamily = f'"{ui_data.ui_font_family}", sans-serif'
     document.documentElement.style.fontSize = ui_data.ui_font_sz
+    runtime.QT_VERSION = ui_data.QT_VERSION
     if view is None:
         create_session_data(prefs, local_storage)
         view = View(document.getElementById('view'))