diff --git a/src/cfdp/pdu/ack.rs b/src/cfdp/pdu/ack.rs
index 38f27d2..1773735 100644
--- a/src/cfdp/pdu/ack.rs
+++ b/src/cfdp/pdu/ack.rs
@@ -7,6 +7,8 @@ use super::{
     add_pdu_crc, generic_length_checks_pdu_deserialization, CfdpPdu, FileDirectiveType, PduError,
     PduHeader, WritablePduPacket,
 };
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
 
 /// ACK PDU abstraction.
 ///