diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5e9fff13c..b4025fd1a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## 44.5.1 [#1359](https://github.com/openfisca/openfisca-core/pull/1359)
+
+#### Bug fixes
+
+- Fix `InYamlTestReform` constructor typing for `reformed_parameters`.
+  - Replace `reformed_parameters=dict` with a proper type annotation and a safe `None` default.
+  - Clarify in the docstring that YAML test `parameters` replaces the full parameter tree.
+
 ## 44.5.0 [#1368](https://github.com/openfisca/openfisca-core/pull/1368)
 
 #### New features
diff --git a/openfisca_core/reforms/in_yaml_test_reform.py b/openfisca_core/reforms/in_yaml_test_reform.py
index 76a7deec1..c8a5855bf 100644
--- a/openfisca_core/reforms/in_yaml_test_reform.py
+++ b/openfisca_core/reforms/in_yaml_test_reform.py
@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+from typing import Any
+
 from openfisca_core.types import TaxBenefitSystem
 
 from openfisca_core.parameters.parameter_node import ParameterNode
@@ -12,18 +14,20 @@ class InYamlTestReform(Reform):
     def __init__(
         self,
         baseline: TaxBenefitSystem,
-        reformed_parameters=dict,
+        reformed_parameters: dict[str, Any] | None = None,
     ) -> None:
-        """Initialize the ReformExcel instance.
+        """Initialize the InYamlTestReform instance.
 
         :param baseline: Baseline TaxBenefitSystem.
-        :param reformed_parameters: Yaml file `parameters` value similar to a parameter tree
+        :param reformed_parameters:
+            YAML test file `parameters` value, shaped like a parameter tree.
+            This reform replaces the full parameter tree with this value.
         """
-        self.reformed_parameters = reformed_parameters
+        self.reformed_parameters = reformed_parameters or {}
         super().__init__(baseline)
 
     def apply(self):
-        def modify_parameters(local_parameters: ParameterNode) -> ParameterNode:
+        def modify_parameters(_local_parameters: ParameterNode) -> ParameterNode:
             return ParameterNode(data=self.reformed_parameters)
 
         self.modify_parameters(modifier_function=modify_parameters)
diff --git a/setup.py b/setup.py
index eb0585e46..856317ed5 100644
--- a/setup.py
+++ b/setup.py
@@ -85,7 +85,7 @@
 
 setup(
     name="OpenFisca-Core",
-    version="44.5.0",
+    version="44.5.1",
     author="OpenFisca Team",
     author_email="contact@openfisca.org",
     classifiers=[