diff --git a/src/calibre/gui2/convert/regex_builder.py b/src/calibre/gui2/convert/regex_builder.py
index b1ea521dc5..c7b03c9bb4 100644
--- a/src/calibre/gui2/convert/regex_builder.py
+++ b/src/calibre/gui2/convert/regex_builder.py
@@ -142,6 +142,8 @@ class RegexBuilder(QDialog, Ui_RegexBuilder):
             try:
                 os.remove(fpath)
             except:
+                # Fails on windows if the input plugin for this format keeps the file open
+                # Happens for LIT files
                 pass
         return True