diff --git a/src/core/devices/nm-device.c b/src/core/devices/nm-device.c
index 0392d54b6a..204cb5c407 100644
--- a/src/core/devices/nm-device.c
+++ b/src/core/devices/nm-device.c
@@ -11816,7 +11816,8 @@ activate_stage3_ip_config(NMDevice *self)
              * IPv6LL if this is not an assumed connection, since assumed connections
              * will already have IPv6 set up.
              */
-            _dev_addrgenmode6_set(self, NM_IN6_ADDR_GEN_MODE_NONE);
+            if (!nm_device_sys_iface_state_is_external_or_assume(self))
+                _dev_addrgenmode6_set(self, NM_IN6_ADDR_GEN_MODE_NONE);
 
             /* Re-enable IPv6 on the interface */
             nm_device_sysctl_ip_conf_set(self, AF_INET6, "accept_ra", "0");