diff --git a/crates/core/src/checkpoint.rs b/crates/core/src/checkpoint.rs
index 9bfdf2eed..e5a5567ea 100644
--- a/crates/core/src/checkpoint.rs
+++ b/crates/core/src/checkpoint.rs
@@ -10,10 +10,12 @@ use crate::BlockId;
 /// Checkpoints are cheaply cloneable and are useful to find the agreement point between two sparse
 /// block chains.
 #[derive(Debug, Clone)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub struct CheckPoint(Arc<CPInner>);
 
 /// The internal contents of [`CheckPoint`].
 #[derive(Debug, Clone)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 struct CPInner {
     /// Block id (hash and height).
     block: BlockId,
diff --git a/crates/core/src/spk_client.rs b/crates/core/src/spk_client.rs
index b6a8e0204..1cbfca6b3 100644
--- a/crates/core/src/spk_client.rs
+++ b/crates/core/src/spk_client.rs
@@ -387,14 +387,14 @@ impl<I> SyncRequest<I> {
 /// See also [`SyncRequest`].
 #[must_use]
 #[derive(Debug)]
-pub struct SyncResponse<A = ConfirmationBlockTime> {
+pub struct SyncResponse<A: Ord = ConfirmationBlockTime> {
     /// Relevant transaction data discovered during the scan.
     pub tx_update: crate::TxUpdate<A>,
     /// Changes to the chain discovered during the scan.
     pub chain_update: Option<CheckPoint>,
 }
 
-impl<A> Default for SyncResponse<A> {
+impl<A: Ord> Default for SyncResponse<A> {
     fn default() -> Self {
         Self {
             tx_update: Default::default(),
@@ -540,7 +540,7 @@ impl<K: Ord + Clone> FullScanRequest<K> {
 /// See also [`FullScanRequest`].
 #[must_use]
 #[derive(Debug)]
-pub struct FullScanResponse<K, A = ConfirmationBlockTime> {
+pub struct FullScanResponse<K, A: Ord = ConfirmationBlockTime> {
     /// Relevant transaction data discovered during the scan.
     pub tx_update: crate::TxUpdate<A>,
     /// Last active indices for the corresponding keychains (`K`). An index is active if it had a
@@ -550,7 +550,7 @@ pub struct FullScanResponse<K, A = ConfirmationBlockTime> {
     pub chain_update: Option<CheckPoint>,
 }
 
-impl<K, A> Default for FullScanResponse<K, A> {
+impl<K, A: Ord> Default for FullScanResponse<K, A> {
     fn default() -> Self {
         Self {
             tx_update: Default::default(),
diff --git a/crates/core/src/tx_update.rs b/crates/core/src/tx_update.rs
index 89a224fbd..b07b20d47 100644
--- a/crates/core/src/tx_update.rs
+++ b/crates/core/src/tx_update.rs
@@ -19,8 +19,9 @@ use bitcoin::{OutPoint, Transaction, TxOut, Txid};
 /// tx_update.anchors.insert((anchor, txid));
 /// ```
 #[derive(Debug, Clone)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[non_exhaustive]
-pub struct TxUpdate<A = ()> {
+pub struct TxUpdate<A: Ord = ()> {
     /// Full transactions. These are transactions that were determined to be relevant to the wallet
     /// given the request.
     pub txs: Vec<Arc<Transaction>>,
@@ -52,7 +53,7 @@ pub struct TxUpdate<A = ()> {
     pub evicted_ats: HashSet<(Txid, u64)>,
 }
 
-impl<A> Default for TxUpdate<A> {
+impl<A: Ord> Default for TxUpdate<A> {
     fn default() -> Self {
         Self {
             txs: Default::default(),