diff --git a/.github/workflows/testing.yml b/.github/workflows/testing.yml
index 3e2ff232..29b6506b 100644
--- a/.github/workflows/testing.yml
+++ b/.github/workflows/testing.yml
@@ -8,11 +8,16 @@ on:
 
 jobs:
   pytest-with-nbmake:
+    strategy:
+      matrix:
+        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
     runs-on: ubuntu-latest
     timeout-minutes: 30
     steps:
     - uses: actions/checkout@v5
     - name: Setup uv project virtual environment
+      env:
+        UV_PYTHON: ${{ matrix.python-version }}
       uses: ./.github/actions/setup-uv
     - name: Run pytest --nbmake
       run: uv run --no-project pytest --nbmake
diff --git a/pyproject.toml b/pyproject.toml
index f0e0f6b8..70d99141 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -71,6 +71,7 @@ jupyter = [
 mypy = [
   "mypy >= 1.14",
   "scipy-stubs >= 1.15; python_version >= '3.10'",
+  "typing_extensions >= 4.10",
 ]
 
 [dependency-groups]
diff --git a/src/rydstate/__init__.py b/src/rydstate/__init__.py
index 7636e437..06216317 100644
--- a/src/rydstate/__init__.py
+++ b/src/rydstate/__init__.py
@@ -12,4 +12,4 @@
 ]
 
 
-__version__ = "0.9.0"
+__version__ = "0.9.1"
diff --git a/src/rydstate/angular/angular_ket.py b/src/rydstate/angular/angular_ket.py
index 1cfc561b..bb01fd3e 100644
--- a/src/rydstate/angular/angular_ket.py
+++ b/src/rydstate/angular/angular_ket.py
@@ -2,7 +2,7 @@
 
 import logging
 from abc import ABC
-from typing import TYPE_CHECKING, Any, ClassVar, Literal, Self, get_args, overload
+from typing import TYPE_CHECKING, Any, ClassVar, Literal, get_args, overload
 
 from rydstate.angular.angular_matrix_element import (
     AngularMomentumQuantumNumbers,
@@ -24,6 +24,8 @@
 from rydstate.species import SpeciesObject
 
 if TYPE_CHECKING:
+    from typing_extensions import Self
+
     from rydstate.angular.angular_state import AngularState
 
 logger = logging.getLogger(__name__)
diff --git a/src/rydstate/angular/angular_state.py b/src/rydstate/angular/angular_state.py
index 2f40acd3..dd054933 100644
--- a/src/rydstate/angular/angular_state.py
+++ b/src/rydstate/angular/angular_state.py
@@ -2,7 +2,7 @@
 
 import logging
 import math
-from typing import TYPE_CHECKING, Any, Generic, Literal, Self, TypeVar, get_args, overload
+from typing import TYPE_CHECKING, Any, Generic, Literal, TypeVar, get_args, overload
 
 import numpy as np
 
@@ -17,10 +17,11 @@
 if TYPE_CHECKING:
     from collections.abc import Iterator
 
+    from typing_extensions import Self
+
     from rydstate.angular.angular_ket import CouplingScheme
     from rydstate.angular.angular_matrix_element import AngularOperatorType
 
-
 logger = logging.getLogger(__name__)
 
 
diff --git a/src/rydstate/angular/utils.py b/src/rydstate/angular/utils.py
index 550afe76..03ad0009 100644
--- a/src/rydstate/angular/utils.py
+++ b/src/rydstate/angular/utils.py
@@ -33,9 +33,9 @@ def sympify_args(func: Callable[P, R]) -> Callable[P, R]:
         return func
 
     def check_arg(arg: float) -> Integer:
-        if arg.is_integer():
+        if isinstance(arg, int) or arg.is_integer():
             return Integer(int(arg))
-        if (arg * 2).is_integer():
+        if isinstance(arg * 2, int) or (arg * 2).is_integer():
             return Integer(int(arg * 2)) / Integer(2)
         raise ValueError(f"Invalid input to {func.__name__}: {arg}.")