diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index 93d4991ddc1f..293d5289c4a1 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -723,9 +723,13 @@ static size_t ovs_flow_cmd_msg_size(const struct sw_flow_actions *acts,
 {
 	size_t len = NLMSG_ALIGN(sizeof(struct ovs_header));
 
-	/* OVS_FLOW_ATTR_UFID */
+	/* OVS_FLOW_ATTR_UFID, or unmasked flow key as fallback
+	 * see ovs_nla_put_identifier()
+	 */
 	if (sfid && ovs_identifier_is_ufid(sfid))
 		len += nla_total_size(sfid->ufid_len);
+	else
+		len += nla_total_size(ovs_key_attr_size());
 
 	/* OVS_FLOW_ATTR_KEY */
 	if (!sfid || should_fill_key(sfid, ufid_flags))