Index: Lib/doctest.py
===================================================================
--- Lib/doctest.py	(revision 67899)
+++ Lib/doctest.py	(working copy)
@@ -1015,7 +1015,7 @@
         if lineno is not None:
             if source_lines is None:
                 return lineno+1
-            pat = re.compile('(^|.*:)\s*\w*("|\')')
+            pat = re.compile('^([^#]*:)?\s*\w*("|\')')
             for lineno in range(lineno, len(source_lines)):
                 if pat.match(source_lines[lineno]):
                     return lineno