diff --git a/hugr-py/src/hugr/serialization/ops.py b/hugr-py/src/hugr/serialization/ops.py
index 660a30f79..85750436e 100644
--- a/hugr-py/src/hugr/serialization/ops.py
+++ b/hugr-py/src/hugr/serialization/ops.py
@@ -3,7 +3,7 @@
 from abc import ABC
 from typing import Any, Literal
 
-from pydantic import Field, RootModel, ConfigDict
+from pydantic import Field, RootModel
 
 from . import tys
 from .tys import (
@@ -73,6 +73,7 @@ class FuncDecl(BaseOp):
 class CustomConst(ConfiguredBaseModel):
     c: str
     v: Any
+
     class Config:
         json_schema_extra = {
             "required": ["c", "v"],
diff --git a/hugr/src/ops/constant.rs b/hugr/src/ops/constant.rs
index a6361511c..4685039bb 100644
--- a/hugr/src/ops/constant.rs
+++ b/hugr/src/ops/constant.rs
@@ -10,11 +10,11 @@ use crate::extension::ExtensionSet;
 use crate::types::{CustomType, EdgeKind, FunctionType, SumType, SumTypeError, Type};
 use crate::{Hugr, HugrView};
 
+use delegate::delegate;
 use itertools::Itertools;
 use serde::{Deserializer, Serializer};
 use smol_str::SmolStr;
 use thiserror::Error;
-use delegate::delegate;
 
 pub use custom::{downcast_equal_consts, CustomConst, CustomSerialized};
 
@@ -81,7 +81,6 @@ impl OpTrait for Const {
     }
 }
 
-
 impl From<Const> for Value {
     fn from(konst: Const) -> Self {
         konst.value
diff --git a/hugr/src/ops/constant/custom.rs b/hugr/src/ops/constant/custom.rs
index fa4a10312..2146d3fd7 100644
--- a/hugr/src/ops/constant/custom.rs
+++ b/hugr/src/ops/constant/custom.rs
@@ -83,7 +83,8 @@ fn deserialize_custom_const<CC: CustomConst>(
         Err(dyn_cc) => {
             // TODO we should return dyn_cc in the error
             Err(<serde_yaml::Error as serde::de::Error>::custom(format!(
-                "Failed to deserialize: {:?}",
+                "Failed to deserialize [{}]: {:?}",
+                std::any::type_name::<CC>(),
                 dyn_cc
             )))
         }
@@ -130,11 +131,11 @@ pub enum CustomSerializedError {
 }
 
 impl CustomSerializedError {
-    fn new_serialize_err(err: serde_yaml::Error, payload: Box<dyn CustomConst>) -> Self {
+    fn new_ser(err: serde_yaml::Error, payload: Box<dyn CustomConst>) -> Self {
         Self::SerializePayloadError { err, payload }
     }
 
-    fn new_deserialize_err(err: serde_yaml::Error, payload: serde_yaml::Value) -> Self {
+    fn new_de(err: serde_yaml::Error, payload: serde_yaml::Value) -> Self {
         Self::DeserializePayloadError { err, payload }
     }
 }
@@ -178,7 +179,7 @@ impl CustomSerialized {
                 let (typ, extension_reqs) = (cc.get_type(), cc.extension_reqs());
                 let value = cc
                     .serialize_dyn_custom_const()
-                    .map_err(|err| CustomSerializedError::new_serialize_err(err, cc))?;
+                    .map_err(|err| CustomSerializedError::new_ser(err, cc))?;
                 Ok(Self::new(typ, value, extension_reqs))
             }
         }
@@ -194,7 +195,7 @@ impl CustomSerialized {
         // ideally we would not have to clone, but serde_json does not allow us
         // to recover the value from the error
         let cc_box = deserialize_dyn_custom_const(value.clone())
-            .map_err(|err| CustomSerializedError::new_deserialize_err(err, value))?;
+            .map_err(|err| CustomSerializedError::new_de(err, value))?;
         assert_eq!(cc_box.get_type(), typ);
         assert_eq!(cc_box.extension_reqs(), extensions);
         Ok(cc_box)
@@ -210,7 +211,7 @@ impl CustomSerialized {
         // ideally we would not have to clone, but serde_json does not allow us
         // to recover the value from the error
         let cc: CC = deserialize_custom_const(value.clone())
-            .map_err(|err| CustomSerializedError::new_deserialize_err(err, value))?;
+            .map_err(|err| CustomSerializedError::new_de(err, value))?;
         assert_eq!(cc.get_type(), typ);
         assert_eq!(cc.extension_reqs(), extensions);
         Ok(cc)
@@ -262,7 +263,7 @@ impl From<CustomSerialized> for Box<dyn CustomConst> {
 
 #[cfg(test)]
 mod test {
-    use serde::{Deserialize, Serialize};
+    
 
     use crate::{
         ops::constant::custom::{