diff --git a/src/calibre/gui2/viewer/web_view.py b/src/calibre/gui2/viewer/web_view.py
index 0237119beb..6251bba3ea 100644
--- a/src/calibre/gui2/viewer/web_view.py
+++ b/src/calibre/gui2/viewer/web_view.py
@@ -317,6 +317,7 @@ def apply_font_settings(page_or_view):
     s.setFontFamily(s.StandardFont, s.fontFamily(sf))
     old_minimum = s.fontSize(s.MinimumFontSize)
     old_base = s.fontSize(s.DefaultFontSize)
+    old_fixed_base = s.fontSize(s.DefaultFixedFontSize)
     mfs = fs.get('minimum_font_size')
     if mfs is None:
         s.resetFontSize(s.MinimumFontSize)
@@ -325,8 +326,10 @@ def apply_font_settings(page_or_view):
     bfs = sd.get('base_font_size')
     if bfs is not None:
         s.setFontSize(s.DefaultFontSize, bfs)
+        s.setFontSize(s.DefaultFixedFontSize, int(bfs * 13 / 16))
 
-    font_size_changed = old_minimum != s.fontSize(s.MinimumFontSize) or old_base != s.fontSize(s.DefaultFontSize)
+    font_size_changed = (old_minimum, old_base, old_fixed_base) != (
+            s.fontSize(s.MinimumFontSize), s.fontSize(s.DefaultFontSize), s.fontSize(s.DefaultFixedFontSize))
     if font_size_changed and hasattr(page_or_view, 'execute_when_ready'):
         page_or_view.execute_when_ready('viewer_font_size_changed')