diff --git a/opportunity.py b/opportunity.py
index 95fe03ea18..094b114869 100644
--- a/opportunity.py
+++ b/opportunity.py
@@ -692,7 +692,7 @@ class SaleOpportunityEmployeeContext(ModelView):
 class SaleOpportunityMonthly(SaleOpportunityReportMixin, ModelSQL, ModelView):
     'Sale Opportunity per Month'
     __name__ = 'sale.opportunity_monthly'
-    year = fields.Char('Year')
+    year = fields.Integer("Year")
     month = fields.Many2One('ir.calendar.month', "Month")
     year_month = fields.Function(fields.Char('Year-Month'),
             'get_year_month')
@@ -714,9 +714,7 @@ class SaleOpportunityMonthly(SaleOpportunityReportMixin, ModelSQL, ModelView):
         query = super(SaleOpportunityMonthly, cls).table_query()
         opportunity, = query.from_
         type_id = cls.id.sql_type().base
-        type_year = cls.year.sql_type().base
-        year_column = Extract('YEAR', opportunity.start_date
-            ).cast(type_year).as_('year')
+        year_column = Extract('YEAR', opportunity.start_date).as_('year')
         month_index = Extract('MONTH', opportunity.start_date)
         query.from_ = opportunity.join(
             month, condition=month_index == month.index)
@@ -734,7 +732,7 @@ class SaleOpportunityEmployeeMonthly(
         SaleOpportunityReportMixin, ModelSQL, ModelView):
     'Sale Opportunity per Employee per Month'
     __name__ = 'sale.opportunity_employee_monthly'
-    year = fields.Char('Year')
+    year = fields.Integer("Year")
     month = fields.Many2One('ir.calendar.month', "Month")
     employee = fields.Many2One('company.employee', 'Employee')
 
@@ -753,9 +751,7 @@ class SaleOpportunityEmployeeMonthly(
         query = super(SaleOpportunityEmployeeMonthly, cls).table_query()
         opportunity, = query.from_
         type_id = cls.id.sql_type().base
-        type_year = cls.year.sql_type().base
-        year_column = Extract('YEAR', opportunity.start_date
-            ).cast(type_year).as_('year')
+        year_column = Extract('YEAR', opportunity.start_date).as_('year')
         month_index = Extract('MONTH', opportunity.start_date)
         query.from_ = opportunity.join(
             month, condition=month_index == month.index)
diff --git a/view/opportunity_employee_monthly_tree.xml b/view/opportunity_employee_monthly_tree.xml
index e6b519ae7f..80298765c2 100644
--- a/view/opportunity_employee_monthly_tree.xml
+++ b/view/opportunity_employee_monthly_tree.xml
@@ -2,7 +2,7 @@
 <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
 this repository contains the full copyright notices and license terms. -->
 <tree>
-    <field name="year"/>
+    <field name="year" grouping="0"/>
     <field name="month" widget="selection"/>
     <field name="employee" expand="1"/>
     <field name="number"/>
diff --git a/view/opportunity_monthly_tree.xml b/view/opportunity_monthly_tree.xml
index 630697adbe..8fca6b6b2e 100644
--- a/view/opportunity_monthly_tree.xml
+++ b/view/opportunity_monthly_tree.xml
@@ -2,7 +2,7 @@
 <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
 this repository contains the full copyright notices and license terms. -->
 <tree>
-    <field name="year"/>
+    <field name="year" grouping="0"/>
     <field name="month" widget="selection"/>
     <field name="number"/>
     <field name="converted"/>