diff --git a/test/test_parsing_group.py b/test/test_parsing_group.py
index ba9a667..9125e90 100644
--- a/test/test_parsing_group.py
+++ b/test/test_parsing_group.py
@@ -382,6 +382,35 @@ def test_reset_values_with_master_and_slaves_default():
     assert cfg.ip_admin_eth0.netmask_admin_eth0 == [None]
 
 
+def test_reset_values_with_master_and_slaves_setitem():
+    ip_admin_eth0 = StrOption('ip_admin_eth0', "ip réseau autorisé", multi=True, default=['192.168.230.145'])
+    netmask_admin_eth0 = StrOption('netmask_admin_eth0', "masque du sous-réseau", multi=True)
+    interface1 = OptionDescription('ip_admin_eth0', '', [ip_admin_eth0, netmask_admin_eth0])
+    interface1.impl_set_group_type(groups.master)
+    maconfig = OptionDescription('toto', '', [interface1])
+    cfg = Config(maconfig)
+    cfg.read_write()
+    owner = cfg.cfgimpl_get_settings().getowner()
+    assert cfg.getowner(ip_admin_eth0) == owners.default
+    assert cfg.getowner(netmask_admin_eth0) == owners.default
+
+    cfg.ip_admin_eth0.ip_admin_eth0.append("192.168.230.146")
+    cfg.ip_admin_eth0.ip_admin_eth0.append("192.168.230.146")
+    cfg.ip_admin_eth0.ip_admin_eth0.append("192.168.230.146")
+    assert cfg.ip_admin_eth0.netmask_admin_eth0[-1] == None
+    assert cfg.ip_admin_eth0.netmask_admin_eth0[3] == None
+    assert cfg.getowner(netmask_admin_eth0, 3) == owners.default
+    cfg.ip_admin_eth0.netmask_admin_eth0[-1] = "255.255.255.0"
+    assert cfg.ip_admin_eth0.netmask_admin_eth0[-1] == "255.255.255.0"
+    assert cfg.ip_admin_eth0.netmask_admin_eth0[3] == "255.255.255.0"
+    assert cfg.getowner(netmask_admin_eth0, 3) == owner
+    #
+    assert cfg.getowner(netmask_admin_eth0, 2) == owners.default
+    cfg.ip_admin_eth0.netmask_admin_eth0[2] = "255.255.0.0"
+    assert cfg.ip_admin_eth0.netmask_admin_eth0[-2] == "255.255.0.0"
+    assert cfg.getowner(netmask_admin_eth0, 2) == owner
+
+
 def test_values_with_master_and_slaves_slave():
     ip_admin_eth0 = StrOption('ip_admin_eth0', "ip réseau autorisé", multi=True)
     netmask_admin_eth0 = StrOption('netmask_admin_eth0', "masque du sous-réseau", multi=True)
diff --git a/tiramisu/value.py b/tiramisu/value.py
index 37d01c2..626c306 100644
--- a/tiramisu/value.py
+++ b/tiramisu/value.py
@@ -725,6 +725,8 @@ class Multi(list):
         context = self._getcontext()
         setting = context.cfgimpl_get_settings()
         setting_properties = setting._getproperties(read_write=False)
+        if index < 0:
+            index = self.__len__() + index
         if 'validator' in setting_properties and validate:
             fake_context = context._gen_fake_values()
             fake_multi = fake_context.cfgimpl_get_values()._get_cached_value(