diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index cf7e0a1..9c86c73 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -10,7 +10,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-20.04, windows-2019, macos-11]
-        python-version: ["3.10", "3.11", "3.12-dev", "pypy3.10"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12-dev", "pypy3.10", "pypy3.9"]
     steps:
         - uses: actions/checkout@v3
         - name: Set up Python ${{ matrix.python-version }}
diff --git a/once.py b/once.py
index 9ed01c2..b79e0af 100644
--- a/once.py
+++ b/once.py
@@ -94,7 +94,8 @@ def __get__(self, obj, cls):
             func = functools.partial(self.func.__func__, cls)
             return functools.partial(self._execute_call_once, func)
         if isinstance(self.func, staticmethod):
-            return functools.partial(self._execute_call_once, self.func)
+            # The additional __func__ is required for python <= 3.9
+            return functools.partial(self._execute_call_once, self.func.__func__)
         return functools.partial(self._execute_call_once, self.func, obj)
 
 
diff --git a/pyproject.toml b/pyproject.toml
index 1495215..629e68f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -23,7 +23,7 @@ authors = [
 description = "Utility for initialization ensuring functions are called only once"
 readme = "README.md"
 license = "MIT"
-requires-python = ">=3.10"
+requires-python = ">=3.8"
 classifiers = [
     "Programming Language :: Python :: 3",
     "License :: OSI Approved :: MIT License",