diff --git a/src/calibre/gui2/tweak_book/preview.py b/src/calibre/gui2/tweak_book/preview.py
index 839cf1be5b..7db9afc9c4 100644
--- a/src/calibre/gui2/tweak_book/preview.py
+++ b/src/calibre/gui2/tweak_book/preview.py
@@ -190,7 +190,7 @@ class UrlSchemeHandler(QWebEngineUrlSchemeHandler):
                 QTimer.singleShot(0, self.check_for_parse)
             else:
                 data = get_data(name)
-                if isinstance(data, type('')):
+                if isinstance(data, unicode_type):
                     data = data.encode('utf-8')
                 mime_type = {
                     # Prevent warning in console about mimetype of fonts
diff --git a/src/pyj/editor.pyj b/src/pyj/editor.pyj
index d33c121472..6ca4dadea8 100644
--- a/src/pyj/editor.pyj
+++ b/src/pyj/editor.pyj
@@ -143,7 +143,8 @@ def live_css(editor_name, sourceline, tags):
     for node in document.querySelectorAll(f'[data-lnum="{sourceline}"]'):
         tn = node.tagName.toLowerCase() if node.tagName else ''
         if tn is not tags[i]:
-            to_python.live_css_data(ans)
+            if to_python.live_css_data:
+                to_python.live_css_data(ans)
             return
         i += 1
         target = node
@@ -162,7 +163,8 @@ def live_css(editor_name, sourceline, tags):
             })
         target = target.parentNode
         ancestor_specificity += 1
-    to_python.live_css_data(ans)
+    if to_python.live_css_data:
+        to_python.live_css_data(ans)
 
 
 document.body.addEventListener('click', onclick, True)