diff --git a/openfisca_core/indexed_enums/config.py b/openfisca_core/indexed_enums/config.py
index f7da69b84..abb8817de 100644
--- a/openfisca_core/indexed_enums/config.py
+++ b/openfisca_core/indexed_enums/config.py
@@ -1,3 +1,6 @@
 import numpy
 
 ENUM_ARRAY_DTYPE = numpy.int16
+
+
+__all__ = ["ENUM_ARRAY_DTYPE"]
diff --git a/openfisca_core/indexed_enums/enum.py b/openfisca_core/indexed_enums/enum.py
index a67cd317c..56f007941 100644
--- a/openfisca_core/indexed_enums/enum.py
+++ b/openfisca_core/indexed_enums/enum.py
@@ -32,7 +32,6 @@ def __init__(self, *__args: object, **__kwargs: object) -> None:
             ``_member_names_`` is undocumented in upstream :class:`enum.Enum`.
 
         """
-
         self.index = len(self._member_names_)
 
     #: Bypass the slow :meth:`enum.Enum.__eq__` method.
@@ -100,3 +99,6 @@ def encode(
             ).astype(ENUM_ARRAY_DTYPE)
 
         return EnumArray(array, cls)
+
+
+__all__ = ["Enum"]
diff --git a/openfisca_core/indexed_enums/enum_array.py b/openfisca_core/indexed_enums/enum_array.py
index a04e28cdb..b40ba0401 100644
--- a/openfisca_core/indexed_enums/enum_array.py
+++ b/openfisca_core/indexed_enums/enum_array.py
@@ -66,14 +66,13 @@ def __eq__(self, other: object) -> bool:
             https://en.wikipedia.org/wiki/Liskov_substitution_principle
 
         """
-
         if other.__class__.__name__ is self.possible_values.__name__:
             return self.view(numpy.ndarray) == other.index
 
         return self.view(numpy.ndarray) == other
 
     def __ne__(self, other: object) -> bool:
-        """Inequality…
+        """Inequality.
 
         Args:
             other: Another :class:`object` to compare to.
@@ -89,10 +88,10 @@ def __ne__(self, other: object) -> bool:
             https://en.wikipedia.org/wiki/Liskov_substitution_principle
 
         """
-
         return numpy.logical_not(self == other)
 
-    def _forbidden_operation(self, other: Any) -> NoReturn:
+    @staticmethod
+    def _forbidden_operation(other: Any) -> NoReturn:
         msg = (
             "Forbidden operation. The only operations allowed on EnumArrays "
             "are '==' and '!='."
@@ -127,7 +126,6 @@ def decode(self) -> numpy.object_:
         Decoded value: enum item
 
         """
-
         return numpy.select(
             [self == item.index for item in self.possible_values],
             list(self.possible_values),
@@ -148,7 +146,6 @@ def decode_to_str(self) -> numpy.str_:
         'free_lodger'  # String identifier
 
         """
-
         return numpy.select(
             [self == item.index for item in self.possible_values],
             [item.name for item in self.possible_values],
@@ -159,3 +156,6 @@ def __repr__(self) -> str:
 
     def __str__(self) -> str:
         return str(self.decode_to_str())
+
+
+__all__ = ["EnumArray"]
diff --git a/setup.py b/setup.py
index 202e5e449..d342bb9f4 100644
--- a/setup.py
+++ b/setup.py
@@ -62,7 +62,7 @@
     "pylint >=3.3.1, <4.0",
     "pylint-per-file-ignores >=1.3.2, <2.0",
     "pyright >=1.1.382, <2.0",
-    "ruff >=0.6.7, <1.0",
+    "ruff >=0.6.9, <1.0",
     "ruff-lsp >=0.0.57, <1.0",
     "xdoctest >=1.2.0, <2.0",
     *api_requirements,
diff --git a/stubs/numexpr/__init__.pyi b/stubs/numexpr/__init__.pyi
index f9ada73c3..931d47ddb 100644
--- a/stubs/numexpr/__init__.pyi
+++ b/stubs/numexpr/__init__.pyi
@@ -4,6 +4,7 @@ import numpy
 
 def evaluate(
     __ex: str,
+    /,
     *__args: object,
     **__kwargs: object,
 ) -> NDArray[numpy.bool_] | NDArray[numpy.int32] | NDArray[numpy.float32]: ...