diff --git a/src/calibre/ebooks/oeb/base.py b/src/calibre/ebooks/oeb/base.py
index a85c77fad4..b25e880f58 100644
--- a/src/calibre/ebooks/oeb/base.py
+++ b/src/calibre/ebooks/oeb/base.py
@@ -351,7 +351,7 @@ OEB_IMAGES        = {GIF_MIME, JPEG_MIME, PNG_MIME, SVG_MIME}
 
 MS_COVER_TYPE = 'other.ms-coverimage-standard'
 
-ENTITY_RE     = re.compile(r'&([a-zA-Z_:][a-zA-Z0-9.-_:]+);')
+ENTITY_RE     = re.compile(r'&([a-zA-Z_:][a-zA-Z0-9._:-]+);')
 COLLAPSE_RE   = re.compile(r'[ \t\r\n\v]+')
 QNAME_RE      = re.compile(r'^[{][^{}]+[}][^{}]+$')
 PREFIXNAME_RE = re.compile(r'^[^:]+[:][^:]+')
diff --git a/src/calibre/gui2/markdown_syntax_highlighter.py b/src/calibre/gui2/markdown_syntax_highlighter.py
index 353a36eb1d..3d3c88f869 100644
--- a/src/calibre/gui2/markdown_syntax_highlighter.py
+++ b/src/calibre/gui2/markdown_syntax_highlighter.py
@@ -6,6 +6,7 @@ import re
 
 from qt.core import QApplication, QBrush, QColor, QFont, QSyntaxHighlighter, QTextCharFormat, QTextCursor, QTextLayout
 
+from calibre.ebooks.oeb.base import ENTITY_RE
 from calibre.gui2.palette import dark_link_color, light_link_color
 
 
@@ -31,7 +32,7 @@ class MarkdownHighlighter(QSyntaxHighlighter):
         'HeaderLine': re.compile(r'(?u)^(-|=)+\s*$'),
         'HR': re.compile(r'(?u)^(\s*(\*|-|_)\s*){3,}$'),
         'Html': re.compile(r'(?u)</?[^/\s].*?(?<!\\)>'),
-        'Entity': re.compile(r'&([A-z]{2,7}|#\d{1,7}|#x[\dA-Fa-f]{1,6});'),
+        'Entity': ENTITY_RE,
     }
 
     key_theme_maps = {
diff --git a/src/calibre/gui2/tweak_book/editor/text.py b/src/calibre/gui2/tweak_book/editor/text.py
index feb2de578b..7ced4feadd 100644
--- a/src/calibre/gui2/tweak_book/editor/text.py
+++ b/src/calibre/gui2/tweak_book/editor/text.py
@@ -823,12 +823,11 @@ class TextEdit(PlainTextEdit):
             return self.text_for_range(c.block(), r)
 
     def select_class_name_at_cursor(self, cursor):
-        valid = re.compile(r'[\w_0-9\-]+', flags=re.UNICODE)
+        valid = re.compile(r'^[\w_-]+$', flags=re.UNICODE)
 
         def keep_going():
             q = cursor.selectedText()
-            m = valid.match(q)
-            return m is not None and m.group() == q
+            return valid.match(q) is not None
 
         def run_loop(forward=True):
             cursor.setPosition(pos)