diff --git a/src/cfdp/pdu/nak.rs b/src/cfdp/pdu/nak.rs
index df13d86..5c1f86c 100644
--- a/src/cfdp/pdu/nak.rs
+++ b/src/cfdp/pdu/nak.rs
@@ -13,6 +13,7 @@ use super::{
 use serde::{Deserialize, Serialize};
 
 #[derive(Debug, PartialEq, Eq, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum SegmentRequests<'a> {
     U32Pairs(&'a [(u32, u32)]),
     U64Pairs(&'a [(u64, u64)]),