diff --git a/install/variables/net.py b/install/variables/net.py
index d5cec22..fa3e28b 100644
--- a/install/variables/net.py
+++ b/install/variables/net.py
@@ -155,6 +155,13 @@ class VariableOsInstallNetData(NetHelper,TableVariable):
         self.help = _("Network interface, DHCP or IP address and network mask "
                       "(example: %s)")%" --iface eth0:192.168.1.1:24"
 
+    def raiseReadonlyIndexError(self,fieldname="",variablename="",
+                                value=""):
+        """
+        Behavior on change readonly index
+        """
+        raise VariableError(_("Network interface %s not found")%value)
+
 class VariableOsInstallNetHostname(NetHelper,Variable):
     """
     Computer hostname