diff --git a/autofit/mapper/model.py b/autofit/mapper/model.py
index 010dcac4a..d24ef82bc 100644
--- a/autofit/mapper/model.py
+++ b/autofit/mapper/model.py
@@ -83,9 +83,28 @@ def __init__(self, label=None, id_=None):
         self._frozen_cache = dict()
         super().__init__(label=label, id_=id_)
 
+    @classmethod
+    def _cached_property_names(cls) -> frozenset:
+        """
+        Return the names of every ``cached_property``-style descriptor
+        declared anywhere in ``cls``'s MRO.
+
+        Used by the ``__dict__``-iteration sites in this module and in
+        ``autofit/mapper/prior_model/`` to exclude cached descriptor values
+        from instance construction, ``ModelInstance.dict``, pickling, and
+        downstream JAX pytree flattening. See PyAutoFit#1300 for the
+        diagnosed leak this defends against.
+        """
+        from autoconf.tools.decorators import cached_property_names
+
+        return cached_property_names(cls)
+
     def __getstate__(self):
+        excluded = type(self)._cached_property_names()
         return {
-            key: value for key, value in self.__dict__.items() if key != "_frozen_cache"
+            key: value
+            for key, value in self.__dict__.items()
+            if key != "_frozen_cache" and key not in excluded
         }
 
     def __setstate__(self, state):
@@ -446,11 +465,13 @@ def __hash__(self):
 
     @property
     def dict(self):
+        excluded = type(self)._cached_property_names()
         return {
             key: value
             for key, value in self.__dict__.items()
             if key not in ("id", "component_number", "item_number")
             and not (isinstance(key, str) and key.startswith("_"))
+            and key not in excluded
         }
 
     def tree_flatten(self) -> Tuple[List, Tuple]:
diff --git a/autofit/mapper/model_object.py b/autofit/mapper/model_object.py
index 641c04e77..3316c7324 100644
--- a/autofit/mapper/model_object.py
+++ b/autofit/mapper/model_object.py
@@ -330,9 +330,20 @@ def dict(self) -> dict:
 
     @property
     def _dict(self):
+        # Pick up any cached_property descriptors declared on the class so
+        # their cached values don't propagate via `Collection.items()` (which
+        # delegates here) or any other downstream consumer. The lookup is
+        # gated on hasattr because ModelObject is the base for the whole
+        # mapper module: a few non-AbstractModel descendants do not carry the
+        # ``_cached_property_names`` classmethod.
+        try:
+            excluded = type(self)._cached_property_names()
+        except AttributeError:
+            excluded = frozenset()
         return {
             key: value
             for key, value in self.__dict__.items()
             if key not in ("component_number", "item_number", "id", "cls", "label")
             and not key.startswith("_")
+            and key not in excluded
         }
diff --git a/autofit/mapper/prior_model/abstract.py b/autofit/mapper/prior_model/abstract.py
index ba9d0ea99..663d9fc69 100644
--- a/autofit/mapper/prior_model/abstract.py
+++ b/autofit/mapper/prior_model/abstract.py
@@ -1275,12 +1275,17 @@ def from_instance(
     def items(self):
         """Return (name, value) pairs for all public, non-internal attributes.
 
-        Excludes private attributes (prefixed with ``_``), ``cls``, and ``id``.
+        Excludes private attributes (prefixed with ``_``), ``cls``, ``id``,
+        and any ``cached_property``-style descriptors declared on the class
+        (see ``AbstractModel._cached_property_names``).
         """
+        excluded = type(self)._cached_property_names()
         return [
             (key, value)
             for key, value in self.__dict__.items()
-            if not key.startswith("_") and key not in ("cls", "id")
+            if not key.startswith("_")
+            and key not in ("cls", "id")
+            and key not in excluded
         ]
 
     @property
diff --git a/autofit/mapper/prior_model/collection.py b/autofit/mapper/prior_model/collection.py
index b06d8878b..5198dfe57 100644
--- a/autofit/mapper/prior_model/collection.py
+++ b/autofit/mapper/prior_model/collection.py
@@ -286,8 +286,9 @@ def _instance_for_arguments(
             A list of instances constructed from the list of prior models.
         """
         result = ModelInstance()
+        excluded = type(self)._cached_property_names()
         for key, value in self.__dict__.items():
-            if key.startswith("_"):
+            if key.startswith("_") or key in excluded:
                 continue
             if isinstance(value, AbstractPriorModel):
                 value = value.instance_for_arguments(
diff --git a/autofit/mapper/prior_model/prior_model.py b/autofit/mapper/prior_model/prior_model.py
index c0153e8ae..e758164e2 100644
--- a/autofit/mapper/prior_model/prior_model.py
+++ b/autofit/mapper/prior_model/prior_model.py
@@ -494,12 +494,14 @@ def _instance_for_arguments(
         else:
             result = self.cls(**constructor_arguments)
 
+        excluded = type(self)._cached_property_names()
         for key, value in self.__dict__.items():
             if (
                 not hasattr(result, key)
                 and not isinstance(value, Prior)
                 and not key == "cls"
                 and not key.startswith("_")
+                and key not in excluded
             ):
                 if isinstance(value, Model):
                     value = value.instance_for_arguments(
diff --git a/test_autofit/mapper/test_parameterization.py b/test_autofit/mapper/test_parameterization.py
index 416c07313..a8e845125 100644
--- a/test_autofit/mapper/test_parameterization.py
+++ b/test_autofit/mapper/test_parameterization.py
@@ -1,3 +1,4 @@
+import functools
 import itertools
 
 import pytest
@@ -176,6 +177,92 @@ def test_parameterization_cache_does_not_leak_into_instance():
         assert not isinstance(child, str)
 
 
+def test_cached_property_names_classmethod_walks_mro():
+    """The ``_cached_property_names`` classmethod on AbstractModel exposes the
+    autoconf ``cached_property_names`` MRO walker. It must pick up
+    descriptors declared on any ancestor and memoise the result on the class."""
+
+    import functools
+
+    import autofit as af
+
+    # Build a synthetic subclass with a cached_property to verify the walker
+    # finds it. We use af.Collection because both AbstractPriorModel and
+    # ModelInstance inherit from AbstractModel.
+    class SyntheticCollection(af.Collection):
+        @functools.cached_property
+        def synthetic_value(self):
+            return "a synthetic cached string"
+
+    names = SyntheticCollection._cached_property_names()
+    assert "synthetic_value" in names
+
+    # Result is memoised on the synthetic class.
+    assert "__cached_property_names_cache__" in SyntheticCollection.__dict__
+
+    # Plain af.Collection (no synthetic_value) has its own cache.
+    base_names = af.Collection._cached_property_names()
+    assert "synthetic_value" not in base_names
+
+
+class _GuardedCollection(af.Collection):
+    """Module-level subclass used by
+    ``test_cached_property_excluded_from_all_dict_walks`` — must live at
+    module scope so ``pickle.dumps`` can locate the class on round-trip."""
+
+    @functools.cached_property
+    def derived(self):
+        return "leaky-string"
+
+
+def test_cached_property_excluded_from_all_dict_walks():
+    """Regression: a future ``@functools.cached_property`` declared anywhere
+    in the model class hierarchy must not surface through any of:
+    ``Collection._instance_for_arguments`` (via ``instance.__dict__``),
+    ``ModelInstance.dict``, ``ModelInstance.tree_flatten()``,
+    ``AbstractModel.items()``, ``ModelObject._dict``, or pickling via
+    ``__getstate__``.
+
+    Covers the class of bug PyAutoFit#1300 fixed for ``parameterization``;
+    this test will fail if a maintainer reintroduces an un-prefixed
+    cached_property on the model hierarchy without the
+    ``_cached_property_names`` defense applied at every site."""
+
+    import pickle
+
+    model = _GuardedCollection(gaussian=af.Model(af.ex.Gaussian))
+
+    # Trigger the cache. After this, model.__dict__["derived"] = "leaky-string".
+    _ = model.derived
+    assert model.__dict__.get("derived") == "leaky-string"
+
+    instance = model.instance_from_prior_medians()
+
+    # Site 1+4: Collection._instance_for_arguments + ModelInstance.dict
+    assert "derived" not in instance.__dict__
+    assert "derived" not in instance.dict
+
+    # Site 4 also feeds tree_flatten — no string leaves.
+    leaves = instance.dict.values()
+    for leaf in leaves:
+        assert not isinstance(leaf, str)
+
+    # Site 3: AbstractModel.items() on the model itself.
+    assert all(key != "derived" for key, _ in model.items())
+
+    # Site 5: __getstate__ drops the cached value from pickles.
+    state = model.__getstate__()
+    assert "derived" not in state
+
+    # Round-trip via pickle: the unpickled model re-computes the cached value,
+    # rather than carrying the pickled string on the wire.
+    blob = pickle.dumps(model)
+    revived = pickle.loads(blob)
+    assert "derived" not in revived.__dict__
+    # Touching it recomputes.
+    assert revived.derived == "leaky-string"
+
+
 def test_integer_attributes():
     model = af.Model(af.ex.Gaussian)