diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 9f18be0..b092bfb 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.10", "3.11", "3.12"]
 
     steps:
       - uses: actions/checkout@v3
diff --git a/README.md b/README.md
index faf0f92..7f20f01 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ of dividing the inverse odds by the booksum [[3](#3)].
 
 # Installation
 
-Requires Python 3.9 or above (including Python 3.13).
+Requires Python 3.10 or above.
 
 ```
 pip install shin
diff --git a/pyproject.toml b/pyproject.toml
index a513225..1277917 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "maturin"
 
 [project]
 name = "shin"
-requires-python = ">=3.9"
+requires-python = ">=3.10"
 classifiers = [
     "Programming Language :: Rust",
     "Programming Language :: Python :: Implementation :: CPython",
@@ -27,7 +27,7 @@ Repository = "https://github.com/mberk/shin"
 python-source = "python"
 
 [tool.mypy]
-python_version = "3.9"
+python_version = "3.10"
 packages = ["shin", "tests"]
 enable_error_code = [
     "explicit-override",
diff --git a/requirements-test.txt b/requirements-test.txt
index c845ae6..0ac9f86 100644
--- a/requirements-test.txt
+++ b/requirements-test.txt
@@ -1,4 +1,4 @@
-black==24.3.0
+black==26.3.1
 mypy==1.8.0
 pytest==7.4.3
 pytest-mypy-plugins==3.0.0