diff --git a/src/calibre/gui2/tweak_book/preview.py b/src/calibre/gui2/tweak_book/preview.py
index 6d892cc62a..8fa184b6f0 100644
--- a/src/calibre/gui2/tweak_book/preview.py
+++ b/src/calibre/gui2/tweak_book/preview.py
@@ -752,11 +752,11 @@ class Preview(QWidget):
         s.setFontSize(QWebEngineSettings.FontSize.MinimumFontSize, tprefs['preview_minimum_font_size'])
         sf, ssf, mf = tprefs['engine_preview_serif_family'], tprefs['engine_preview_sans_family'], tprefs['engine_preview_mono_family']
         if sf:
-            s.setFontFamily(s.SerifFont, sf)
+            s.setFontFamily(QWebEngineSettings.FontFamily.SerifFont, sf)
         if ssf:
-            s.setFontFamily(s.SansSerifFont, ssf)
+            s.setFontFamily(QWebEngineSettings.FontFamily.SansSerifFont, ssf)
         if mf:
-            s.setFontFamily(s.FixedFont, mf)
+            s.setFontFamily(QWebEngineSettings.FontFamily.FixedFont, mf)
         stdfnt = tprefs['preview_standard_font_family'] or 'serif'
         stdfnt = getattr(s, {'serif': 'SerifFont', 'sans': 'SansSerifFont', 'mono': 'FixedFont'}[stdfnt])
-        s.setFontFamily(s.StandardFont, s.fontFamily(stdfnt))
+        s.setFontFamily(QWebEngineSettings.FontFamily.StandardFont, s.fontFamily(stdfnt))
diff --git a/src/calibre/gui2/viewer/web_view.py b/src/calibre/gui2/viewer/web_view.py
index 8f772c42bf..1f2ca206c2 100644
--- a/src/calibre/gui2/viewer/web_view.py
+++ b/src/calibre/gui2/viewer/web_view.py
@@ -297,20 +297,20 @@ def apply_font_settings(page_or_view):
     sd = vprefs['session_data']
     fs = sd.get('standalone_font_settings', {})
     if fs.get('serif_family'):
-        s.setFontFamily(s.SerifFont, fs.get('serif_family'))
+        s.setFontFamily(QWebEngineSettings.FontFamily.SerifFont, fs.get('serif_family'))
     else:
-        s.resetFontFamily(s.SerifFont)
+        s.resetFontFamily(QWebEngineSettings.FontFamily.SerifFont)
     if fs.get('sans_family'):
-        s.setFontFamily(s.SansSerifFont, fs.get('sans_family'))
+        s.setFontFamily(QWebEngineSettings.FontFamily.SansSerifFont, fs.get('sans_family'))
     else:
-        s.resetFontFamily(s.SansSerifFont)
+        s.resetFontFamily(QWebEngineSettings.FontFamily.SansSerifFont)
     if fs.get('mono_family'):
-        s.setFontFamily(s.FixedFont, fs.get('mono_family'))
+        s.setFontFamily(QWebEngineSettings.FontFamily.FixedFont, fs.get('mono_family'))
     else:
-        s.resetFontFamily(s.SansSerifFont)
+        s.resetFontFamily(QWebEngineSettings.FontFamily.SansSerifFont)
     sf = fs.get('standard_font') or 'serif'
     sf = getattr(s, {'serif': 'SerifFont', 'sans': 'SansSerifFont', 'mono': 'FixedFont'}[sf])
-    s.setFontFamily(s.StandardFont, s.fontFamily(sf))
+    s.setFontFamily(QWebEngineSettings.FontFamily.StandardFont, s.fontFamily(sf))
     old_minimum = s.fontSize(QWebEngineSettings.FontSize.MinimumFontSize)
     old_base = s.fontSize(QWebEngineSettings.FontSize.DefaultFontSize)
     old_fixed_base = s.fontSize(QWebEngineSettings.FontSize.DefaultFixedFontSize)