diff --git a/purchase.py b/purchase.py
index c0423011f3..99c75cb5d0 100644
--- a/purchase.py
+++ b/purchase.py
@@ -1,5 +1,6 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
+from trytond.model import fields
 from trytond.pool import Pool, PoolMeta
 
 from trytond.modules.analytic_account import AnalyticMixin
@@ -16,21 +17,30 @@ class Purchase:
         super(Purchase, cls).__setup__()
         cls._error_messages.update({
                 'analytic_account_required': ('Analytic account is required '
-                    'on line "%s".'),
+                    'for "%(roots)s" on line "%(line)s".'),
                 })
 
     def check_for_quotation(self):
         pool = Pool()
-        AnalyticAccountEntry = pool.get('analytic.account.entry')
+        Account = pool.get('analytic_account.account')
+        mandatory_roots = {a for a in Account.search([
+                ('type', '=', 'root'),
+                ('mandatory', '=', True),
+                ])}
 
         super(Purchase, self).check_for_quotation()
 
         for line in self.lines:
             if line.type != 'line':
                 continue
-            if not AnalyticAccountEntry.check_root(line.analytic_accounts):
-                self.raise_user_error('analytic_account_required',
-                    line.rec_name)
+            analytic_roots = {e.root for e in line.analytic_accounts
+                if e.account}
+            if not mandatory_roots <= analytic_roots:
+                self.raise_user_error('analytic_account_required', {
+                        'line': line.rec_name,
+                        'roots': ', '.join(x.rec_name
+                            for x in mandatory_roots - analytic_roots),
+                        })
 
 
 class PurchaseLine(AnalyticMixin):
@@ -58,3 +68,14 @@ class AnalyticAccountEntry:
     def _get_origin(cls):
         origins = super(AnalyticAccountEntry, cls)._get_origin()
         return origins + ['purchase.line']
+
+    @fields.depends('origin')
+    def on_change_with_required(self, name=None):
+        pool = Pool()
+        PurchaseLine = pool.get('purchase.line')
+        required = super(AnalyticAccountEntry, self).on_change_with_required(
+            name)
+        if (self.origin and isinstance(self.origin, PurchaseLine)
+                and self.origin.purchase.state in ['cancel', 'draft']):
+            return False
+        return required