diff --git a/linera-base/src/identifiers.rs b/linera-base/src/identifiers.rs
index 3767b7ac6ff..912b4b5aded 100644
--- a/linera-base/src/identifiers.rs
+++ b/linera-base/src/identifiers.rs
@@ -13,7 +13,7 @@ use std::{
 use anyhow::{anyhow, Context};
 use async_graphql::SimpleObject;
 use linera_witty::{WitLoad, WitStore, WitType};
-use serde::{Deserialize, Serialize};
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
 
 use crate::{
     bcs_scalar,
@@ -201,21 +201,7 @@ impl From<&BlobContent> for BlobType {
 }
 
 /// A content-addressed blob ID i.e. the hash of the `BlobContent`.
-#[derive(
-    Eq,
-    PartialEq,
-    Ord,
-    PartialOrd,
-    Clone,
-    Copy,
-    Hash,
-    Debug,
-    Serialize,
-    Deserialize,
-    WitType,
-    WitStore,
-    WitLoad,
-)]
+#[derive(Eq, PartialEq, Ord, PartialOrd, Clone, Copy, Hash, Debug, WitType, WitStore, WitLoad)]
 #[cfg_attr(with_testing, derive(test_strategy::Arbitrary, Default))]
 pub struct BlobId {
     /// The hash of the blob.
@@ -263,6 +249,45 @@ impl FromStr for BlobId {
     }
 }
 
+#[derive(Serialize, Deserialize)]
+#[serde(rename = "BlobId")]
+struct BlobIdHelper {
+    hash: CryptoHash,
+    blob_type: BlobType,
+}
+
+impl Serialize for BlobId {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        if serializer.is_human_readable() {
+            serializer.serialize_str(&self.to_string())
+        } else {
+            let helper = BlobIdHelper {
+                hash: self.hash,
+                blob_type: self.blob_type,
+            };
+            helper.serialize(serializer)
+        }
+    }
+}
+
+impl<'a> Deserialize<'a> for BlobId {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'a>,
+    {
+        if deserializer.is_human_readable() {
+            let s = String::deserialize(deserializer)?;
+            Self::from_str(&s).map_err(serde::de::Error::custom)
+        } else {
+            let helper = BlobIdHelper::deserialize(deserializer)?;
+            Ok(BlobId::new(helper.hash, helper.blob_type))
+        }
+    }
+}
+
 /// The index of a message in a chain.
 #[derive(
     Eq,
diff --git a/linera-client/src/util.rs b/linera-client/src/util.rs
index ce7ac4508b6..e3a4e4d173a 100644
--- a/linera-client/src/util.rs
+++ b/linera-client/src/util.rs
@@ -66,38 +66,3 @@ macro_rules! impl_from_infallible {
 
 pub(crate) use impl_from_dynamic;
 pub(crate) use impl_from_infallible;
-
-pub mod serde_btreemap_keys_as_strings {
-    use std::{collections::BTreeMap, fmt::Display, str::FromStr};
-
-    use serde::{self, Deserialize, Deserializer, Serialize, Serializer};
-
-    pub fn serialize<K, V, S>(map: &BTreeMap<K, V>, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        K: Display,
-        V: Serialize,
-        S: Serializer,
-    {
-        let string_map: BTreeMap<String, &V> =
-            map.iter().map(|(k, v)| (k.to_string(), v)).collect();
-        string_map.serialize(serializer)
-    }
-
-    pub fn deserialize<'de, K, V, D>(deserializer: D) -> Result<BTreeMap<K, V>, D::Error>
-    where
-        K: FromStr + Ord,
-        <K as FromStr>::Err: Display,
-        V: Deserialize<'de>,
-        D: Deserializer<'de>,
-    {
-        let string_map: BTreeMap<String, V> = BTreeMap::deserialize(deserializer)?;
-        string_map
-            .into_iter()
-            .map(|(k, v)| {
-                k.parse()
-                    .map(|key| (key, v))
-                    .map_err(serde::de::Error::custom)
-            })
-            .collect()
-    }
-}
diff --git a/linera-client/src/wallet.rs b/linera-client/src/wallet.rs
index 3588511980a..79a0f0fddda 100644
--- a/linera-client/src/wallet.rs
+++ b/linera-client/src/wallet.rs
@@ -18,7 +18,7 @@ use linera_storage::Storage;
 use rand::Rng as _;
 use serde::{Deserialize, Serialize};
 
-use crate::{config::GenesisConfig, error, util::serde_btreemap_keys_as_strings, Error};
+use crate::{config::GenesisConfig, error, Error};
 
 #[derive(Serialize, Deserialize)]
 pub struct Wallet {
@@ -210,7 +210,6 @@ pub struct UserChain {
     pub timestamp: Timestamp,
     pub next_block_height: BlockHeight,
     pub pending_block: Option<Block>,
-    #[serde(with = "serde_btreemap_keys_as_strings")]
     pub pending_blobs: BTreeMap<BlobId, Blob>,
 }