diff --git a/src/calibre/gui2/widgets.py b/src/calibre/gui2/widgets.py
index ed5b89dcbb..f2c55472c4 100644
--- a/src/calibre/gui2/widgets.py
+++ b/src/calibre/gui2/widgets.py
@@ -14,6 +14,7 @@ from PyQt5.Qt import (QIcon, QFont, QLabel, QListWidget, QAction,
         QLineEdit, QComboBox, QPen, QGraphicsScene, QMenu, QStringListModel,
         QCompleter, QTimer, QRect, QGraphicsView, QPagedPaintDevice)
 
+from calibre.constants import iswindows, isosx
 from calibre.gui2 import (error_dialog, pixmap_to_data, gprefs,
         warning_dialog)
 from calibre.gui2.filename_pattern_ui import Ui_Form
@@ -1243,7 +1244,11 @@ class PaperSizes(QComboBox):  # {{{
     def initialize(self, choices=None):
         from calibre.utils.icu import numeric_sort_key
         if self.system_default_paper_size is None:
-            QComboBox.system_default_paper_size = 'letter' if QPrinter().pageSize() == QPagedPaintDevice.Letter else 'a4'
+            PaperSizes.system_default_paper_size = 'a4'
+            if iswindows or isosx:
+                # On Linux, this can cause Qt to load the system cups plugin
+                # which can crash: https://bugs.launchpad.net/calibre/+bug/1861741
+                PaperSizes.system_default_paper_size = 'letter' if QPrinter().pageSize() == QPagedPaintDevice.Letter else 'a4'
         if not choices:
             from calibre.ebooks.conversion.plugins.pdf_output import PAPER_SIZES
             choices = PAPER_SIZES
@@ -1260,7 +1265,7 @@ class PaperSizes(QComboBox):  # {{{
 
     @get_value_for_config.setter
     def set_value_for_config(self, val):
-        idx = self.findData(val or self.system_default_paper_size)
+        idx = self.findData(val or PaperSizes.system_default_paper_size)
         if idx == -1:
             idx = self.findData('a4')
         self.setCurrentIndex(idx)