diff --git a/CHANGELOG b/CHANGELOG
index 325b864912..90e14a17bf 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,6 @@
 * Add cached_property in tools
 * Use custom class to store record data
+* Do not write to existing targets on xxx2Many add
 * Add configuration check
 * Add support for properties to fields.depends
 * Allow combining authentication methods together
diff --git a/trytond/model/fields/one2many.py b/trytond/model/fields/one2many.py
index d0155b0a4d..14145e1d5c 100644
--- a/trytond/model/fields/one2many.py
+++ b/trytond/model/fields/one2many.py
@@ -173,6 +173,14 @@ class One2Many(Field):
             else:
                 return record_id
 
+        def target_value(record):
+            if record is None:
+                return None
+            if field._type == 'reference':
+                return str(record)
+            else:
+                return record.id
+
         def create(ids, vlist):
             for record_id in ids:
                 value = field_value(record_id)
@@ -195,9 +203,13 @@ class One2Many(Field):
                 return
             targets = Target.browse(target_ids)
             for record_id in ids:
-                to_write.extend((targets, {
-                            self.field: field_value(record_id),
-                            }))
+                fvalue = field_value(record_id)
+                to_update = [t for t in targets
+                    if target_value(getattr(t, self.field)) != fvalue]
+                if to_update:
+                    to_write.extend((to_update, {
+                                self.field: fvalue,
+                                }))
 
         def remove(ids, target_ids):
             target_ids = list(map(int, target_ids))
diff --git a/trytond/tests/test_field_many2many.py b/trytond/tests/test_field_many2many.py
index 5008295b33..8a42d44043 100644
--- a/trytond/tests/test_field_many2many.py
+++ b/trytond/tests/test_field_many2many.py
@@ -309,6 +309,25 @@ class CommonTestCaseMixin:
         self.assertTupleEqual(many2many.targets, (target2,))
         self.assertListEqual(targets, [target2])
 
+    @with_transaction()
+    def test_write_not_readd(self):
+        "Test write many2many do not re-add existing"
+        pool = Pool()
+        Many2Many = self.Many2Many()
+        Relation = pool.get(Many2Many.targets.relation_name)
+        many2many, = Many2Many.create([{
+                    'targets': [('create', [{}])],
+                    }])
+
+        target, = many2many.targets
+
+        Many2Many.write([many2many], {
+                    'targets': [('add', {target.id})],
+                    })
+
+        relation, = Relation.search([])
+        self.assertIsNone(relation.write_date)
+
 
 class FieldMany2ManyTestCase(unittest.TestCase, CommonTestCaseMixin):
     "Test Field Many2Many"
diff --git a/trytond/tests/test_field_one2many.py b/trytond/tests/test_field_one2many.py
index 9366b0c825..7abe51490a 100644
--- a/trytond/tests/test_field_one2many.py
+++ b/trytond/tests/test_field_one2many.py
@@ -370,6 +370,23 @@ class CommonTestCaseMixin:
         self.assertTupleEqual(one2many.targets, (target2,))
         self.assertListEqual(targets, [target2])
 
+    @with_transaction()
+    def test_write_not_readd(self):
+        "Test write one2many do not re-add existing"
+        One2Many = self.One2Many()
+        one2many, = One2Many.create([{
+                    'targets': [('create', [{}])],
+                    }])
+
+        target, = one2many.targets
+
+        One2Many.write([one2many], {
+                    'targets': [('add', {target.id})],
+                    })
+
+        target, = one2many.targets
+        self.assertIsNone(target.write_date)
+
 
 class FieldOne2ManyTestCase(unittest.TestCase, CommonTestCaseMixin):
     "Test Field One2Many"