diff --git a/src/calibre/library/catalogs/epub_mobi_builder.py b/src/calibre/library/catalogs/epub_mobi_builder.py
index 591b965c8d..6e3da4bbf4 100644
--- a/src/calibre/library/catalogs/epub_mobi_builder.py
+++ b/src/calibre/library/catalogs/epub_mobi_builder.py
@@ -1364,28 +1364,19 @@ class CatalogBuilder:
         else:
             return None
 
-    def format_prefix(self, prefix_char):
+    def insert_prefix(self, soup, parent_tag, pos, prefix_char):
         """ Generate HTML snippet with prefix character.
 
-        Return a <code> snippet for Kindle, <span> snippet for EPUB.
+        Insert a <code> snippet for Kindle, <span> snippet for EPUB.
         Optimized to preserve first-column alignment for MOBI, EPUB.
-
-        Args:
-         prefix_char (str): prefix character or None
-
-        Return:
-         (str): BeautifulSoup HTML snippet to be inserted into <p> line item entry.
         """
-
-        prefix_char = prepare_string_for_xml(prefix_char or NBSP)
         if self.opts.fmt == 'mobi':
-            tagname = 'code'
-            html = f'<{tagname}>{prefix_char}</{tagname}>'
+            tag = soup.new_tag('code')
         else:
-            tagname = 'span'
-            html =  f'<{tagname} class="prefix">{prefix_char}</{tagname}>'
-        soup = BeautifulSoup(html)
-        return soup.find(tagname)
+            tag = soup.new_tag('span')
+            tag['class'] = 'prefix'
+        tag.append(prefix_char or NBSP)
+        parent_tag.insert(pos, tag)
 
     def generate_author_anchor(self, author):
         """ Generate legal XHTML anchor.
@@ -1566,7 +1557,7 @@ class CatalogBuilder:
             pBookTag['class'] = "line_item"
             ptc = 0
 
-            pBookTag.insert(ptc, self.format_prefix(book['prefix']))
+            self.insert_prefix(soup, pBookTag, ptc, book['prefix'])
             ptc += 1
 
             spanTag = soup.new_tag("span")
@@ -1717,7 +1708,7 @@ class CatalogBuilder:
                     pBookTag['class'] = "line_item"
                     ptc = 0
 
-                    pBookTag.insert(ptc, self.format_prefix(new_entry['prefix']))
+                    self.insert_prefix(soup, pBookTag, ptc, new_entry['prefix'])
                     ptc += 1
 
                     spanTag = soup.new_tag("span")
@@ -1769,7 +1760,7 @@ class CatalogBuilder:
                     pBookTag['class'] = "line_item"
                     ptc = 0
 
-                    pBookTag.insert(ptc, self.format_prefix(new_entry['prefix']))
+                    self.insert_prefix(soup, pBookTag, ptc, new_entry['prefix'])
                     ptc += 1
 
                     spanTag = soup.new_tag("span")
@@ -2285,7 +2276,7 @@ class CatalogBuilder:
             pBookTag['class'] = "line_item"
             ptc = 0
 
-            pBookTag.insert(ptc, self.format_prefix(book['prefix']))
+            self.insert_prefix(soup, pBookTag, ptc, book['prefix'])
             ptc += 1
 
             spanTag = soup.new_tag("span")
@@ -2418,7 +2409,7 @@ class CatalogBuilder:
             ptc = 0
 
             book['prefix'] = self.discover_prefix(book)
-            pBookTag.insert(ptc, self.format_prefix(book['prefix']))
+            self.insert_prefix(soup, pBookTag, ptc, book['prefix'])
             ptc += 1
 
             spanTag = soup.new_tag("span")
@@ -2577,7 +2568,7 @@ class CatalogBuilder:
             pBookTag['class'] = "line_item"
             ptc = 0
 
-            pBookTag.insert(ptc, self.format_prefix(book['prefix']))
+            self.insert_prefix(soup, pBookTag, ptc, book['prefix'])
             ptc += 1
 
             spanTag = soup.new_tag("span")