diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c
index 63ec0a21889ae4c585cda6d3f056036f410c267a..a80bc3fe3a9d570d1b9157511a77e798cb847713 100644
--- a/src/libxl/libxl_driver.c
+++ b/src/libxl/libxl_driver.c
@@ -4096,6 +4096,31 @@ libxlDomainUpdateDeviceConfig(virDomainDefPtr vmdef, virDomainDeviceDefPtr dev)
 }
 
 
+static void
+libxlDomainAttachDeviceNormalize(const virDomainDeviceDef *devConf,
+                                 virDomainDeviceDefPtr devLive)
+{
+    /*
+     * Fixup anything that needs to be identical in the live and
+     * config versions of DeviceDef, but might not be. Do this by
+     * changing the contents of devLive. This is done after all
+     * post-parse tweaks and validation, so be very careful about what
+     * changes are made.
+     */
+
+    /* MAC address should be identical in both DeviceDefs, but if it
+     * wasn't specified in the XML, and was instead autogenerated, it
+     * will be different for the two since they are each the result of
+     * a separate parser call. If it *was* specified, it will already
+     * be the same, so copying does no harm.
+     */
+
+    if (devConf->type == VIR_DOMAIN_DEVICE_NET)
+        virMacAddrSet(&devLive->data.net->mac, &devConf->data.net->mac);
+
+}
+
+
 static int
 libxlDomainAttachDeviceFlags(virDomainPtr dom, const char *xml,
                              unsigned int flags)
@@ -4104,7 +4129,9 @@ libxlDomainAttachDeviceFlags(virDomainPtr dom, const char *xml,
     libxlDriverConfigPtr cfg = libxlDriverConfigGet(driver);
     virDomainObjPtr vm = NULL;
     virDomainDefPtr vmdef = NULL;
-    virDomainDeviceDefPtr dev = NULL;
+    virDomainDeviceDefPtr devConf = NULL;
+    virDomainDeviceDef devConfSave = { 0 };
+    virDomainDeviceDefPtr devLive = NULL;
     int ret = -1;
 
     virCheckFlags(VIR_DOMAIN_DEVICE_MODIFY_LIVE |
@@ -4123,28 +4150,36 @@ libxlDomainAttachDeviceFlags(virDomainPtr dom, const char *xml,
         goto endjob;
 
     if (flags & VIR_DOMAIN_DEVICE_MODIFY_CONFIG) {
-        if (!(dev = virDomainDeviceDefParse(xml, vm->def,
-                                            driver->xmlopt, NULL,
-                                            VIR_DOMAIN_DEF_PARSE_INACTIVE)))
+        if (!(devConf = virDomainDeviceDefParse(xml, vm->def,
+                                                driver->xmlopt, NULL,
+                                                VIR_DOMAIN_DEF_PARSE_INACTIVE)))
             goto endjob;
 
         /* Make a copy for updated domain. */
         if (!(vmdef = virDomainObjCopyPersistentDef(vm, driver->xmlopt, NULL)))
             goto endjob;
 
-        if (libxlDomainAttachDeviceConfig(vmdef, dev) < 0)
+        /*
+         * devConf will be NULLed out by
+         * libxlDomainAttachDeviceConfig(), so save it for later use by
+         * libxlDomainAttachDeviceNormalize()
+         */
+        devConfSave = *devConf;
+
+        if (libxlDomainAttachDeviceConfig(vmdef, devConf) < 0)
             goto endjob;
     }
 
     if (flags & VIR_DOMAIN_DEVICE_MODIFY_LIVE) {
-        /* If dev exists it was created to modify the domain config. Free it. */
-        virDomainDeviceDefFree(dev);
-        if (!(dev = virDomainDeviceDefParse(xml, vm->def,
+        if (!(devLive = virDomainDeviceDefParse(xml, vm->def,
                                             driver->xmlopt, NULL,
                                             VIR_DOMAIN_DEF_PARSE_INACTIVE)))
             goto endjob;
 
-        if (libxlDomainAttachDeviceLive(driver, vm, dev) < 0)
+        if (flags & VIR_DOMAIN_AFFECT_CONFIG)
+            libxlDomainAttachDeviceNormalize(&devConfSave, devLive);
+
+        if (libxlDomainAttachDeviceLive(driver, vm, devLive) < 0)
             goto endjob;
 
         /*
@@ -4171,7 +4206,8 @@ libxlDomainAttachDeviceFlags(virDomainPtr dom, const char *xml,
 
  cleanup:
     virDomainDefFree(vmdef);
-    virDomainDeviceDefFree(dev);
+    virDomainDeviceDefFree(devConf);
+    virDomainDeviceDefFree(devLive);
     virDomainObjEndAPI(&vm);
     virObjectUnref(cfg);
     return ret;