diff --git a/addons/project_issue/report/project_issue_report.py b/addons/project_issue/report/project_issue_report.py
index b550b5c47ce..ee0712f3cac 100644
--- a/addons/project_issue/report/project_issue_report.py
+++ b/addons/project_issue/report/project_issue_report.py
@@ -53,8 +53,8 @@ class project_issue_report(osv.osv):
         'categ_id': fields.many2one('crm.case.categ', 'Category', domain="[('section_id','=',section_id),('object_id.model', '=', 'project.issue')]"),
         'type_id': fields.many2one('project.task.type', 'Stage'),
         'nbr': fields.integer('# of Issues', readonly=True),
-        'working_hours_open': fields.float('Avg. Working Hours to Open', readonly=True),
-        'working_hours_close': fields.float('Avg. Working Hours to Close', readonly=True),
+        'working_hours_open': fields.float('Avg. Working Hours to Open', readonly=True, group_operator="avg"),
+        'working_hours_close': fields.float('Avg. Working Hours to Close', readonly=True, group_operator="avg"),
         'delay_open': fields.float('Avg. Delay to Open', digits=(16,2), readonly=True, group_operator="avg",
                                        help="Number of Days to close the project issue"),
         'delay_close': fields.float('Avg. Delay to Close', digits=(16,2), readonly=True, group_operator="avg",