diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3a89a4f..3ce1257 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -23,7 +23,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v5
         with:
-          python-version: 3.9
+          python-version: "3.10"
           cache: 'pip'
           cache-dependency-path: pyproject.toml
 
@@ -44,7 +44,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v5
         with:
-          python-version: 3.9
+          python-version: "3.10"
 
       - name: Install Python packages
         run: |
@@ -68,7 +68,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu-22.04, macos-12, windows-2022 ]
-        python: [ 3.9, "3.10", "3.11", "3.12" ]
+        python: [ "3.10", "3.11", "3.12" ]
     env:
       GCC_V: 11
     steps:
diff --git a/pyproject.toml b/pyproject.toml
index 2260648..fa38197 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -28,13 +28,12 @@ classifiers = [
     "Intended Audience :: Science/Research",
     "License :: CC0 1.0 Universal (CC0 1.0) Public Domain Dedication",
     "Programming Language :: Python :: 3 :: Only",
-    "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
     "Topic :: Scientific/Engineering :: Hydrology",
 ]
-requires-python = ">=3.9"
+requires-python = ">=3.10"
 dependencies = [
     "attrs",  # todo: bounds?
     "cattrs",  # todo: bounds?