diff --git a/liquidation.py b/liquidation.py
index fd18a65..83508dc 100644
--- a/liquidation.py
+++ b/liquidation.py
@@ -809,10 +809,10 @@ class LiquidationLine(ModelSQL, ModelView):
             table_h.drop_column('hoard_amount')
         super(LiquidationLine, cls).__register__(module_name)
 
-    @fields.depends('wage_type')
+    @fields.depends('wage')
     def on_change_with_is_wage_tax(self, name=None):
-        if self.wage_type:
-            return self.wage_type.type_concept == 'tax'
+        if self.wage:
+            return self.wage.type_concept == 'tax'
         return False
 
     def get_party(self, name=None):
diff --git a/payroll.py b/payroll.py
index 4610361..7ffa51b 100644
--- a/payroll.py
+++ b/payroll.py
@@ -198,31 +198,32 @@ class Payroll(metaclass=PoolMeta):
         end_date = None
         self.contract = contract
         contract_end_date = None
+        contract_start_date = contract.start_date
         if contract:
             if not contract.finished_date:
                 end_date = period_end
 
-                if period_start >= contract.start_date:
+                if period_start >= contract_start_date:
                     start_date = period_start
-                elif contract.start_date >= period_start and \
-                        contract.start_date <= period_end:
-                    start_date = contract.start_date
+                elif contract_start_date >= period_start and \
+                        contract_start_date <= period_end:
+                    start_date = contract_start_date
             else:
                 contract_end_date = contract.finished_date if contract.finished_date else contract.end_date
-                if contract.start_date <= period_start and \
+                if contract_start_date <= period_start and \
                         contract_end_date >= period_end:
                     start_date = period_start
                     end_date = period_end
-                elif contract.start_date >= period_start and \
+                elif contract_start_date >= period_start and \
                         contract_end_date <= period_end:
-                    start_date = contract.start_date
+                    start_date = contract_start_date
                     end_date = contract_end_date
-                elif contract.start_date >= period_start and \
-                        contract.start_date <= period_end and \
+                elif contract_start_date >= period_start and \
+                        contract_start_date <= period_end and \
                         contract_end_date >= period_end:
-                    start_date = contract.start_date
+                    start_date = contract_start_date
                     end_date = period_end
-                elif contract.start_date <= period_start and \
+                elif contract_start_date <= period_start and \
                         contract_end_date >= period_start and \
                         contract_end_date <= period_end:
                     start_date = period_start