diff --git a/baybe/surrogates/base.py b/baybe/surrogates/base.py
index 166e5d0c34..6c9885e603 100644
--- a/baybe/surrogates/base.py
+++ b/baybe/surrogates/base.py
@@ -7,6 +7,13 @@
 
 from attrs import define, field
 from cattrs import override
+from cattrs.dispatch import (
+    StructuredValue,
+    StructureHook,
+    TargetType,
+    UnstructuredValue,
+    UnstructureHook,
+)
 
 from baybe.searchspace import SearchSpace
 from baybe.serialization import SerialMixin, converter, unstructure_base
@@ -160,33 +167,35 @@ def _fit(self, searchspace: SearchSpace, train_x: Tensor, train_y: Tensor) -> No
         """
 
 
-def _decode_onnx_str(raw_unstructure_hook):
+def _decode_onnx_str(raw_unstructure_hook: UnstructureHook) -> UnstructureHook:
     """Decode ONNX string for serialization purposes."""
 
-    def wrapper(obj):
-        dict_ = raw_unstructure_hook(obj)
-        if "onnx_str" in dict_:
-            dict_["onnx_str"] = dict_["onnx_str"].decode(_ONNX_ENCODING)
+    def wrapper(obj: StructuredValue) -> UnstructuredValue:
+        dct = raw_unstructure_hook(obj)
+        if "onnx_str" in dct:
+            dct["onnx_str"] = dct["onnx_str"].decode(_ONNX_ENCODING)
 
-        return dict_
+        return dct
 
     return wrapper
 
 
-def _encode_onnx_str(raw_structure_hook):
+def _encode_onnx_str(raw_structure_hook: StructureHook) -> StructureHook:
     """Encode ONNX string for deserialization purposes."""
 
-    def wrapper(dict_, _):
-        if (onnx_str := dict_.get("onnx_str")) and isinstance(onnx_str, str):
-            dict_["onnx_str"] = onnx_str.encode(_ONNX_ENCODING)
-        obj = raw_structure_hook(dict_, _)
+    def wrapper(dct: UnstructuredValue, _: TargetType) -> StructuredValue:
+        if (onnx_str := dct.get("onnx_str")) and isinstance(onnx_str, str):
+            dct["onnx_str"] = onnx_str.encode(_ONNX_ENCODING)
+        obj = raw_structure_hook(dct, _)
 
         return obj
 
     return wrapper
 
 
-def _block_serialize_custom_architecture(raw_unstructure_hook):
+def _block_serialize_custom_architecture(
+    raw_unstructure_hook: UnstructureHook
+) -> UnstructureHook:
     """Raise error if attempt to serialize a custom architecture surrogate."""
     # TODO: Ideally, this hook should be removed and unstructuring the Surrogate
     #   base class should automatically invoke the blocking hook that is already
@@ -196,7 +205,7 @@ def _block_serialize_custom_architecture(raw_unstructure_hook):
     #   because the role of the subclass will probably be replaced with a surrogate
     #   protocol.
 
-    def wrapper(obj):
+    def wrapper(obj: StructuredValue) -> UnstructuredValue:
         if obj.__class__.__name__ == "CustomArchitectureSurrogate":
             raise NotImplementedError(
                 "Serializing objects of type 'CustomArchitectureSurrogate' "