diff --git a/src/calibre/gui2/tweak_book/editor/smarts/html.py b/src/calibre/gui2/tweak_book/editor/smarts/html.py
index 6d03a04355..aee0d952f3 100644
--- a/src/calibre/gui2/tweak_book/editor/smarts/html.py
+++ b/src/calibre/gui2/tweak_book/editor/smarts/html.py
@@ -488,15 +488,17 @@ class Smarts(NullSmarts):
         editor.setTextCursor(c)
 
     def insert_tag(self, editor, name):
+        m = re.match(r'[a-zA-Z0-9:-]+', name)
+        cname = name if m is None else m.group()
+        self.surround_with_custom_tag(editor, f'<{name}>', f'</{cname}>')
+
+    def surround_with_custom_tag(self, editor, opent, close):
         editor.highlighter.join()
-        name = name.lstrip()
         text = self.get_smart_selection(editor, update=True)
         c = editor.textCursor()
         pos = min(c.position(), c.anchor())
-        m = re.match(r'[a-zA-Z0-9:-]+', name)
-        cname = name if m is None else m.group()
-        c.insertText(f'<{name}>{text}</{cname}>')
-        c.setPosition(pos + 2 + len(name))
+        c.insertText(f'{opent}{text}{close}')
+        c.setPosition(pos + len(opent))
         editor.setTextCursor(c)
 
     def verify_for_spellcheck(self, cursor, highlighter):
diff --git a/src/calibre/gui2/tweak_book/editor/text.py b/src/calibre/gui2/tweak_book/editor/text.py
index 974e977e3b..a8c0541bfa 100644
--- a/src/calibre/gui2/tweak_book/editor/text.py
+++ b/src/calibre/gui2/tweak_book/editor/text.py
@@ -871,19 +871,8 @@ class TextEdit(PlainTextEdit):
             'color': ('<span style="color: %s">' % color, '</span>'),
             'background-color': ('<span style="background-color: %s">' % color, '</span>'),
         }[formatting]
-        left, right = self.get_range_inside_tag()
-        c = self.textCursor()
-        c.setPosition(left)
-        c.setPosition(right, QTextCursor.MoveMode.KeepAnchor)
-        prev_text = str(c.selectedText()).rstrip('\0')
-        c.insertText(prefix + prev_text + suffix)
-        if prev_text:
-            right = c.position()
-            c.setPosition(left)
-            c.setPosition(right, QTextCursor.MoveMode.KeepAnchor)
-        else:
-            c.setPosition(c.position() - len(suffix))
-        self.setTextCursor(c)
+        if hasattr(self.smarts, 'surround_with_custom_tag'):
+            self.smarts.surround_with_custom_tag(self, prefix, suffix)
 
     def insert_image(self, href, fullpage=False, preserve_aspect_ratio=False, width=-1, height=-1):
         if width <= 0: