diff --git a/src/calibre/library/comments.py b/src/calibre/library/comments.py
index 1e312d5b5b..21320e28cc 100644
--- a/src/calibre/library/comments.py
+++ b/src/calibre/library/comments.py
@@ -135,6 +135,8 @@ def markdown(val):
         from calibre.ebooks.markdown import Markdown
         md = markdown.Markdown = Markdown()
     val = md.convert(val)
+    # The Qt Rich text widgets display <p><br></p> as two blank lines instead
+    # of one so fix that here.
     return re.sub(r'<p(|\s+[^>]*?)>\s*<br\s*/?>\s*</p>','<p\\1>\xa0</p>', val)