diff --git a/trieste/models/gpflux/models.py b/trieste/models/gpflux/models.py
index 8f685f580d..b311d41322 100644
--- a/trieste/models/gpflux/models.py
+++ b/trieste/models/gpflux/models.py
@@ -212,6 +212,10 @@ def __getstate__(self) -> dict[str, Any]:
             finally:
                 self._model_keras.history.model = history_model
 
+        # don't try to serialize any other copies of the history callback
+        if isinstance(state.get("_last_optimization_result"), keras.callbacks.History):
+            state["_last_optimization_result"] = ...
+
         return state
 
     def __setstate__(self, state: dict[str, Any]) -> None:
@@ -265,6 +269,8 @@ def __setstate__(self, state: dict[str, Any]) -> None:
                 model = tf.keras.models.model_from_json(model_json)
                 model.set_weights(weights)
                 self._model_keras.history.set_model(model)
+            if state.get("_last_optimization_result") is ...:
+                self._last_optimization_result = self._model_keras.history
 
     def __repr__(self) -> str:
         """"""
diff --git a/trieste/models/keras/architectures.py b/trieste/models/keras/architectures.py
index 06dad5931f..7fc19385d0 100644
--- a/trieste/models/keras/architectures.py
+++ b/trieste/models/keras/architectures.py
@@ -22,6 +22,7 @@
 from typing import Any, Callable, Sequence
 
 import dill
+import keras.callbacks
 import numpy as np
 import tensorflow as tf
 import tensorflow_probability as tfp
@@ -127,6 +128,10 @@ def __getstate__(self) -> dict[str, Any]:
             finally:
                 self._model.history.model = history_model
 
+        # Don't try to serialize any other copies of the history callback
+        if isinstance(state.get("_last_optimization_result"), keras.callbacks.History):
+            state["_last_optimization_result"] = ...
+
         return state
 
     def __setstate__(self, state: dict[str, Any]) -> None:
@@ -150,6 +155,8 @@ def __setstate__(self, state: dict[str, Any]) -> None:
                 )
                 model.set_weights(weights)
                 self._model.history.set_model(model)
+            if state.get("_last_optimization_result") is ...:
+                self._last_optimization_result = self._model.history
 
 
 class KerasEnsembleNetwork: