=== trac/ticket/report.py
==================================================================
--- trac/ticket/report.py	(revision 8619)
+++ trac/ticket/report.py	(local)
@@ -22,6 +22,7 @@
 from trac import util
 from trac.core import *
 from trac.perm import IPermissionRequestor
+from trac.util import sorted
 from trac.web import IRequestHandler
 from trac.web.chrome import add_link, add_stylesheet, INavigationContributor
 from trac.wiki import wiki_to_html, IWikiSyntaxProvider, Formatter
@@ -314,7 +315,7 @@
                 else:
                     sorter = ColumnSorter(colIndex)
                     req.hdf[k] = 1
-                rows.sort(sorter.sort)
+                rows = sorted(rows, cmp=sorter.sort)
 
         # Convert the rows and cells to HDF-format
         row_idx = 0