diff --git a/src/calibre/gui2/markdown_syntax_highlighter.py b/src/calibre/gui2/markdown_syntax_highlighter.py
index 5bb0c5d10a..c481773647 100644
--- a/src/calibre/gui2/markdown_syntax_highlighter.py
+++ b/src/calibre/gui2/markdown_syntax_highlighter.py
@@ -22,13 +22,13 @@ class MarkdownHighlighter(QSyntaxHighlighter):
         'uBoldItalic': re.compile(r'(?<!\\)(?P<delim>___)(?P<text>([^_]{2,}?|[^_]))(?<!\\)(?P=delim)'),
         'Link': re.compile(r'(?<![!\\]])\[.*?(?<!\\)\](\[.+?(?<!\\)\]|\(.+?(?<!\\)\))'),
         'Image': re.compile(r'(?<!\\)!\[.*?(?<!\\)\](\[.+?(?<!\\)\]|\(.+?(?<!\\)\))'),
-        'LinkRef': re.compile(r'^(?u)^\s*\[.*?\]:\s*[^\s].*'),
+        'LinkRef': re.compile(r'(?u)^\s*\[.*?\]:\s*[^\s].*'),
         'Header': re.compile(r'^#{1,6}.*'),
         'UnorderedList': re.compile(r'(?u)^\s*(\*|\+|-)[ \t]\s*'),
         'UnorderedListStar': re.compile(r'(?u)^\s*\*[ \t]\s*'),
         'OrderedList': re.compile(r'(?u)^\s*\d+\.[ \t]\s*'),
         'BlockQuote': re.compile(r'^[ ]{0,3}>+[ \t]?'),
-        'CodeBlock': re.compile('^([ ]{4,}|[ ]*\t).*'),
+        'CodeBlock': re.compile(r'^([ ]{4,}|[ ]*\t).*'),
         'CodeSpan': re.compile(r'(?<!\\)(?P<delim>`+).+?(?P=delim)'),
         'HeaderLine': re.compile(r'(?u)^(-|=)+\s*$'),
         'HR': re.compile(r'(?u)^(\s*(\*|-|_)\s*){3,}$'),