diff --git a/src/calibre/ebooks/conversion/plugins/pdf_output.py b/src/calibre/ebooks/conversion/plugins/pdf_output.py
index 4ff6480a1b..9f35284f28 100644
--- a/src/calibre/ebooks/conversion/plugins/pdf_output.py
+++ b/src/calibre/ebooks/conversion/plugins/pdf_output.py
@@ -56,14 +56,14 @@ class PDFOutput(OutputFormatPlugin):
                 ' of stretching it to fill the full first page of the'
                 ' generated pdf.')),
         OptionRecommendation(name='pdf_serif_family',
-            recommended_value='Liberation Serif', help=_(
-                'The font family used to render serif fonts')),
+            recommended_value='Times', help=_(
+                'The font family used to render serif fonts. Will work only if the font is available system-wide.')),
         OptionRecommendation(name='pdf_sans_family',
-            recommended_value='Liberation Sans', help=_(
-                'The font family used to render sans-serif fonts')),
+            recommended_value='Helvetica', help=_(
+                'The font family used to render sans-serif fonts. Will work only if the font is available system-wide.')),
         OptionRecommendation(name='pdf_mono_family',
-            recommended_value='Liberation Mono', help=_(
-                'The font family used to render monospace fonts')),
+            recommended_value='Courier', help=_(
+                'The font family used to render monospace fonts. Will work only if the font is available system-wide.')),
         OptionRecommendation(name='pdf_standard_font', choices=ui_data['font_types'],
             recommended_value='serif', help=_(
                 'The font family used to render monospace fonts')),
@@ -134,14 +134,13 @@ class PDFOutput(OutputFormatPlugin):
         # that hopefully no Qt application has been constructed as yet
         from PyQt5.QtWebEngineCore import QWebEngineUrlScheme
         from PyQt5.QtWebEngineWidgets import QWebEnginePage  # noqa
-        from calibre.gui2 import must_use_qt, load_builtin_fonts
+        from calibre.gui2 import must_use_qt
         from calibre.constants import FAKE_PROTOCOL
         scheme = QWebEngineUrlScheme(FAKE_PROTOCOL.encode('ascii'))
         scheme.setSyntax(QWebEngineUrlScheme.Syntax.Host)
         scheme.setFlags(QWebEngineUrlScheme.SecureScheme)
         QWebEngineUrlScheme.registerScheme(scheme)
         must_use_qt()
-        load_builtin_fonts()
         self.input_fmt = input_fmt
 
         if opts.pdf_use_document_margins:
diff --git a/src/calibre/gui2/__init__.py b/src/calibre/gui2/__init__.py
index 47127936eb..726e711107 100644
--- a/src/calibre/gui2/__init__.py
+++ b/src/calibre/gui2/__init__.py
@@ -747,22 +747,22 @@ class Translator(QTranslator):
 
 
 gui_thread = None
-
 qt_app = None
 
-builtin_fonts_loaded = False
+
+def calibre_font_files():
+    return glob.glob(P('fonts/liberation/*.?tf')) + [P('fonts/calibreSymbols.otf')] + \
+            glob.glob(os.path.join(config_dir, 'fonts', '*.?tf'))
 
 
 def load_builtin_fonts():
     global _rating_font, builtin_fonts_loaded
     # Load the builtin fonts and any fonts added to calibre by the user to
     # Qt
-    if builtin_fonts_loaded:
+    if hasattr(load_builtin_fonts, 'done'):
         return
-    builtin_fonts_loaded = True
-    for ff in glob.glob(P('fonts/liberation/*.?tf')) + \
-            [P('fonts/calibreSymbols.otf')] + \
-            glob.glob(os.path.join(config_dir, 'fonts', '*.?tf')):
+    load_builtin_fonts.done = True
+    for ff in calibre_font_files():
         if ff.rpartition('.')[-1].lower() in {'ttf', 'otf'}:
             with open(ff, 'rb') as s:
                 # Windows requires font files to be executable for them to be