diff --git a/src/calibre/gui2/comments_editor.py b/src/calibre/gui2/comments_editor.py
index db64bce0a3..6ca08a8e64 100644
--- a/src/calibre/gui2/comments_editor.py
+++ b/src/calibre/gui2/comments_editor.py
@@ -17,7 +17,7 @@ from PyQt5.Qt import (
     QHBoxLayout, QIcon, QKeySequence, QLabel, QLineEdit, QMenu, QPalette,
     QPlainTextEdit, QPushButton, QSize, QSyntaxHighlighter, Qt, QTabWidget,
     QTextBlockFormat, QTextCharFormat, QTextCursor, QTextEdit, QTextListFormat,
-    QToolBar, QUrl, QVBoxLayout, QWidget, pyqtSignal, pyqtSlot, QToolButton
+    QToolBar, QUrl, QVBoxLayout, QWidget, pyqtSignal, pyqtSlot, QToolButton, QTextFormat
 )
 
 from calibre import xml_replace_entities
@@ -558,11 +558,11 @@ class EditorWidget(QTextEdit, LineEditECM):  # {{{
             bf.setTopMargin(tmargin), bf.setBottomMargin(bmargin)
             bf.setHeadingLevel(lvl)
             if adjust:
-                bcf.setProperty(QTextCharFormat.FontSizeAdjustment, adjust)
-                cf.setProperty(QTextCharFormat.FontSizeAdjustment, adjust)
+                bcf.setProperty(QTextFormat.Property.FontSizeAdjustment, adjust)
+                cf.setProperty(QTextFormat.Property.FontSizeAdjustment, adjust)
             if wt:
-                bcf.setProperty(QTextCharFormat.FontWeight, wt)
-                cf.setProperty(QTextCharFormat.FontWeight, wt)
+                bcf.setProperty(QTextFormat.Property.FontWeight, wt)
+                cf.setProperty(QTextFormat.Property.FontWeight, wt)
             c.setBlockCharFormat(bcf)
             c.mergeCharFormat(cf)
             c.mergeBlockFormat(bf)
diff --git a/src/calibre/gui2/tweak_book/editor/__init__.py b/src/calibre/gui2/tweak_book/editor/__init__.py
index 0c11c32fdb..573e5be9f6 100644
--- a/src/calibre/gui2/tweak_book/editor/__init__.py
+++ b/src/calibre/gui2/tweak_book/editor/__init__.py
@@ -5,7 +5,7 @@
 __license__ = 'GPL v3'
 __copyright__ = '2013, Kovid Goyal <kovid at kovidgoyal.net>'
 
-from PyQt5.Qt import QTextCharFormat
+from PyQt5.Qt import QTextCharFormat, QTextFormat
 
 from calibre.ebooks.oeb.base import OEB_DOCS, OEB_STYLES
 from calibre.ebooks.oeb.polish.container import guess_type
@@ -42,7 +42,7 @@ def editor_from_syntax(syntax, parent=None):
         return Editor(syntax, parent=parent)
 
 
-SYNTAX_PROPERTY = QTextCharFormat.UserProperty
+SYNTAX_PROPERTY = QTextFormat.Property.UserProperty
 SPELL_PROPERTY = SYNTAX_PROPERTY + 1
 SPELL_LOCALE_PROPERTY = SPELL_PROPERTY + 1
 LINK_PROPERTY = SPELL_LOCALE_PROPERTY + 1