diff --git a/openfisca_core/populations/_core_population.py b/openfisca_core/populations/_core_population.py
index cead5687b..0f0d968ce 100644
--- a/openfisca_core/populations/_core_population.py
+++ b/openfisca_core/populations/_core_population.py
@@ -28,7 +28,7 @@ class CorePopulation:
     """Base class to build populations from.
 
     Args:
-        entity: The :class:`.CoreEntity` of the population.
+        entity: The :class:`~entities.CoreEntity` of the population.
         *__args: Variable length argument list.
         **__kwds: Arbitrary keyword arguments.
 
@@ -43,7 +43,7 @@ class CorePopulation:
     #: A pseudo index for the members of the population.
     ids: Sequence[str] = []
 
-    #: The :class:`.Simulation` for which the population is calculated.
+    #: The :class:`~simulations.Simulation` for which the population is calculated.
     simulation: None | t.Simulation = None
 
     #: The holders of the variables.
@@ -67,7 +67,7 @@ def __call__(
             options: The options to use for the calculation.
 
         Returns:
-            None: If there is no :class:`.Simulation`.
+            None: If there is no :class:`~simulations.Simulation`.
             ndarray[generic]: The result of the calculation.
 
         Raises:
diff --git a/openfisca_core/populations/_errors.py b/openfisca_core/populations/_errors.py
index a8c64916f..69bda1a5a 100644
--- a/openfisca_core/populations/_errors.py
+++ b/openfisca_core/populations/_errors.py
@@ -1,11 +1,13 @@
 from openfisca_core import types as t
 
+from ._enums import Option
+
 
 class IncompatibleOptionsError(ValueError):
     """Raised when two options are incompatible."""
 
     def __init__(self, variable_name: t.VariableName) -> None:
-        add, divide = t.Option
+        add, divide = Option
         msg = (
             f"Options {add} and {divide} are incompatible (trying to compute "
             f"variable {variable_name})."
diff --git a/openfisca_core/reforms/reform.py b/openfisca_core/reforms/reform.py
index 76e715233..1f0b0ed38 100644
--- a/openfisca_core/reforms/reform.py
+++ b/openfisca_core/reforms/reform.py
@@ -71,7 +71,8 @@ def modify_parameters(self, modifier_function):
         Call this function in `apply()` if the reform asks for legislation parameter modifications.
 
         Args:
-            modifier_function: A function that takes a :obj:`.ParameterNode` and should return an object of the same type.
+            modifier_function: A function that takes a :obj:`~parameters.ParameterNode` and should return an object of
+            the same type.
 
         """
         baseline_parameters = self.baseline.parameters
diff --git a/openfisca_core/types.py b/openfisca_core/types.py
index 50f3b5e85..4d781e122 100644
--- a/openfisca_core/types.py
+++ b/openfisca_core/types.py
@@ -321,9 +321,6 @@ def __getitem__(self, __index: str | VarArray, /) -> ParameterNodeChild: ...
 #: For example 2020.
 PeriodInt = NewType("PeriodInt", int)
 
-#: Type alias for a period-like object.
-PeriodLike: TypeAlias = Union["Period", "PeriodStr", PeriodInt]
-
 
 class _InstantStrMeta(type):
     def __instancecheck__(self, arg: object) -> bool:
@@ -406,15 +403,15 @@ def offset(
     ) -> Period: ...
 
 
+#: Type alias for a period-like object.
+PeriodLike: TypeAlias = Union[Period, PeriodStr, PeriodInt]
+
+
 # Populations
 
 #: Type alias for a population's holders.
 HolderByVariable: TypeAlias = MutableMapping["VariableName", Holder[_N]]
 
-# TODO(Mauko Quiroga-Alvarado): I'm not sure if this type alias is correct.
-# https://openfisca.org/doc/coding-the-legislation/50_entities.html
-Members: TypeAlias = Iterable["SinglePopulation"]
-
 
 class MemoryUsageByVariable(TypedDict, total=False):
     by_variable: dict[VariableName, MemoryUsage]
@@ -448,6 +445,11 @@ def members_entity_id(self, /) -> StrArray: ...
     def nb_persons(self, /, __role: None | Role = ...) -> int: ...
 
 
+# TODO(Mauko Quiroga-Alvarado): I'm not sure if this type alias is correct.
+# https://openfisca.org/doc/coding-the-legislation/50_entities.html
+Members: TypeAlias = Iterable[SinglePopulation]
+
+
 # Simulations
 
 
@@ -507,9 +509,6 @@ def instantiate_entities(self, /) -> dict[str, CorePopulation]: ...
 #: A type representing a mapping of serialized traces.
 SerializedNodeMap: TypeAlias = dict["NodeKey", "SerializedTraceMap"]
 
-#: A stack of simple traces.
-SimpleStack: TypeAlias = list["SimpleTraceMap"]
-
 #: Key of a trace.
 NodeKey = NewType("NodeKey", str)
 
@@ -587,6 +586,10 @@ def formula_time(self, /) -> Time: ...
     def append_child(self, __node: TraceNode, /) -> None: ...
 
 
+#: A stack of simple traces.
+SimpleStack: TypeAlias = list[SimpleTraceMap]
+
+
 # Variables
 
 #: For example "salary".