diff --git a/src/calibre/ebooks/conversion/preprocess.py b/src/calibre/ebooks/conversion/preprocess.py
index c3ed86ce79..061d8ae2b1 100644
--- a/src/calibre/ebooks/conversion/preprocess.py
+++ b/src/calibre/ebooks/conversion/preprocess.py
@@ -602,7 +602,7 @@ class HTMLPreProcessor(object):
                 end_rules.append(
                     # Un wrap using punctuation
                     (re.compile((
-                        r'(?<=.{%i}([a-zäëïöüàèìòùáćéíĺóŕńśúýâêîôûçąężıãõñæøþðßěľščťžňďřů,:)\\IA\u00DF]'
+                        r'(?<=.{%i}([a-zäëïöüàèìòùáćéíĺóŕńśúýâêîôûçąężıãõñæøþðßěľščťžňďřů,:)\\IAß]'
                         r'|(?<!\&\w{4});))\s*(?P<ital></(i|b|u)>)?\s*(</p>\s*<p>\s*)+\s*(?=(<(i|b|u)>)?'
                         r'\s*[\w\d$(])') % length, re.UNICODE), wrap_lines),
                 )
diff --git a/src/calibre/ebooks/conversion/utils.py b/src/calibre/ebooks/conversion/utils.py
index 6d509094ab..991c560d23 100644
--- a/src/calibre/ebooks/conversion/utils.py
+++ b/src/calibre/ebooks/conversion/utils.py
@@ -367,7 +367,7 @@ class HeuristicProcessor(object):
 
         # define the pieces of the regex
         # (?<!\&\w{4});) is a semicolon not part of an entity
-        lookahead = "(?<=.{"+unicode_type(length)+"}([a-zა-ჰäëïöüàèìòùáćéíĺóŕńśúýâêîôûçąężıãõñæøþðßěľščťžňďřů,:)\\IA\u00DF]|(?<!\\&\\w{4});))"
+        lookahead = "(?<=.{"+unicode_type(length)+r"}([a-zა-ჰäëïöüàèìòùáćéíĺóŕńśúýâêîôûçąężıãõñæøþðßěľščťžňďřů,:)\\IAß]|(?<!\&\w{4});))"
         em_en_lookahead = "(?<=.{"+unicode_type(length)+"}[\u2013\u2014])"
         soft_hyphen = "\xad"
         line_ending = "\\s*(?P<style_close></(span|[iub])>)?\\s*(</(p|div)>)?"