diff --git a/src/calibre/ebooks/conversion/utils.py b/src/calibre/ebooks/conversion/utils.py
index aabb1b8bc4..ad7f5f117d 100644
--- a/src/calibre/ebooks/conversion/utils.py
+++ b/src/calibre/ebooks/conversion/utils.py
@@ -137,17 +137,17 @@ class HeuristicProcessor(object):
         ]
 
         ITALICIZE_STYLE_PATS = [
-            r'(?msu)(?<=\s)_(?P<words>\S[^_]{0,40}?\S)?_(?=\s)',
-            r'(?msu)(?<=\s)/(?P<words>\S[^/]{0,40}?\S)?/(?=\s)',
-            r'(?msu)(?<=\s)~~(?P<words>\S[^~]{0,40}?\S)?~~(?=\s)',
-            r'(?msu)(?<=\s)\*(?P<words>\S[^\*]{0,40}?\S)?\*(?=\s)',
-            r'(?msu)(?<=\s)~(?P<words>\S[^~]{0,40}?\S)?~(?=\s)',
-            r'(?msu)(?<=\s)_/(?P<words>\S[^/_]{0,40}?\S)?/_(?=\s)',
-            r'(?msu)(?<=\s)_\*(?P<words>\S[^\*_]{0,40}?\S)?\*_(?=\s)',
-            r'(?msu)(?<=\s)\*/(?P<words>\S[^/\*]{0,40}?\S)?/\*(?=\s)',
-            r'(?msu)(?<=\s)_\*/(?P<words>\S[^\*_]{0,40}?\S)?/\*_(?=\s)',
-            r'(?msu)(?<=\s)/:(?P<words>\S[^:/]{0,40}?\S)?:/(?=\s)',
-            r'(?msu)(?<=\s)\|:(?P<words>\S[^:\|]{0,40}?\S)?:\|(?=\s)',
+            r'(?msu)(?<=\s)_(?P<words>\S[^_]{0,40}?\S)?_(?=[\s\.,\!\?])',
+            r'(?msu)(?<=\s)/(?P<words>\S[^/]{0,40}?\S)?/(?=[\s\.,\!\?])',
+            r'(?msu)(?<=\s)~~(?P<words>\S[^~]{0,40}?\S)?~~(?=[\s\.,\!\?])',
+            r'(?msu)(?<=\s)\*(?P<words>\S[^\*]{0,40}?\S)?\*(?=[\s\.,\!\?])',
+            r'(?msu)(?<=\s)~(?P<words>\S[^~]{0,40}?\S)?~(?=[\s\.,\!\?])',
+            r'(?msu)(?<=\s)_/(?P<words>\S[^/_]{0,40}?\S)?/_(?=[\s\.,\!\?])',
+            r'(?msu)(?<=\s)_\*(?P<words>\S[^\*_]{0,40}?\S)?\*_(?=[\s\.,\!\?])',
+            r'(?msu)(?<=\s)\*/(?P<words>\S[^/\*]{0,40}?\S)?/\*(?=[\s\.,\!\?])',
+            r'(?msu)(?<=\s)_\*/(?P<words>\S[^\*_]{0,40}?\S)?/\*_(?=[\s\.,\!\?])',
+            r'(?msu)(?<=\s)/:(?P<words>\S[^:/]{0,40}?\S)?:/(?=[\s\.,\!\?])',
+            r'(?msu)(?<=\s)\|:(?P<words>\S[^:\|]{0,40}?\S)?:\|(?=[\s\.,\!\?])',
         ]
 
         for word in ITALICIZE_WORDS: