diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 03a8c41..f59842f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -38,7 +38,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [macos-latest, windows-latest, ubuntu-latest]
-        python-version: ["3.10", "3.11", "3.12-dev"]
+        python-version: ["3.10", "3.11", "3.12", "pypy3.10"]
 
     runs-on: ${{ matrix.os }}
     name: ${{ fromJson('{"macos-latest":"macOS","windows-latest":"Windows","ubuntu-latest":"Ubuntu"}')[matrix.os] }} Python ${{ matrix.python-version }}
@@ -49,9 +49,10 @@ jobs:
         uses: actions/checkout@v3
 
       - name: Setup Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v3
+        uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python-version }}
+          allow-prereleases: true
 
       - name: Setup Go
         uses: actions/setup-go@v3
diff --git a/pyproject.toml b/pyproject.toml
index ac871dc..fb56453 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -11,7 +11,7 @@ authors = [
 readme = "README.md"
 license = {file = "LICENSE"}
 classifiers = [
-  "Development Status :: 4 - Beta",
+  "Development Status :: 5 - Production/Stable",
   "Intended Audience :: Developers",
   "License :: OSI Approved :: MIT License",
   "Operating System :: MacOS",
@@ -21,6 +21,8 @@ classifiers = [
   "Programming Language :: Python :: 3.10",
   "Programming Language :: Python :: 3.11",
   "Programming Language :: Python :: 3.12",
+  "Programming Language :: Python :: Implementation :: CPython",
+  "Programming Language :: Python :: Implementation :: PyPy",
 ]
 dynamic = ["version", "description"]
 requires-python = ">= 3.10"
diff --git a/src/truststore/_api.py b/src/truststore/_api.py
index 571ea3c..3c28065 100644
--- a/src/truststore/_api.py
+++ b/src/truststore/_api.py
@@ -6,7 +6,12 @@
 
 import _ssl  # type: ignore[import]
 
-from ._ssl_constants import _original_SSLContext, _original_super_SSLContext
+from ._ssl_constants import (
+    _original_SSLContext,
+    _original_super_SSLContext,
+    _truststore_SSLContext_dunder_class,
+    _truststore_SSLContext_super_class,
+)
 
 if platform.system() == "Windows":
     from ._windows import _configure_context, _verify_peercerts_impl
@@ -49,9 +54,16 @@ def extract_from_ssl() -> None:
         pass
 
 
-class SSLContext(ssl.SSLContext):
+class SSLContext(_truststore_SSLContext_super_class):  # type: ignore[misc]
     """SSLContext API that uses system certificates on all platforms"""
 
+    @property  # type: ignore[misc]
+    def __class__(self) -> type:
+        # Dirty hack to get around isinstance() checks
+        # for ssl.SSLContext instances in aiohttp/trustme
+        # when using non-CPython implementations.
+        return _truststore_SSLContext_dunder_class or SSLContext
+
     def __init__(self, protocol: int = None) -> None:  # type: ignore[assignment]
         self._ctx = _original_SSLContext(protocol)
 
@@ -240,7 +252,7 @@ def protocol(self) -> ssl._SSLMethod:
         return self._ctx.protocol
 
     @property
-    def security_level(self) -> int:  # type: ignore[override]
+    def security_level(self) -> int:
         return self._ctx.security_level
 
     @property
diff --git a/src/truststore/_ssl_constants.py b/src/truststore/_ssl_constants.py
index be60f83..b1ee7a3 100644
--- a/src/truststore/_ssl_constants.py
+++ b/src/truststore/_ssl_constants.py
@@ -1,10 +1,29 @@
 import ssl
+import sys
+import typing
 
 # Hold on to the original class so we can create it consistently
 # even if we inject our own SSLContext into the ssl module.
 _original_SSLContext = ssl.SSLContext
 _original_super_SSLContext = super(_original_SSLContext, _original_SSLContext)
 
+# CPython is known to be good, but non-CPython implementations
+# may implement SSLContext differently so to be safe we don't
+# subclass the SSLContext.
+
+# This is returned by truststore.SSLContext.__class__()
+_truststore_SSLContext_dunder_class: typing.Optional[type]
+
+# This value is the superclass of truststore.SSLContext.
+_truststore_SSLContext_super_class: type
+
+if sys.implementation.name == "cpython":
+    _truststore_SSLContext_super_class = _original_SSLContext
+    _truststore_SSLContext_dunder_class = None
+else:
+    _truststore_SSLContext_super_class = object
+    _truststore_SSLContext_dunder_class = _original_SSLContext
+
 
 def _set_ssl_context_verify_mode(
     ssl_context: ssl.SSLContext, verify_mode: ssl.VerifyMode
diff --git a/tests/conftest.py b/tests/conftest.py
index c9b23a2..938611c 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -140,9 +140,13 @@ async def handler(request: web.Request) -> web.Response:
     app.add_routes([web.get("/", handler)])
 
     ctx = original_SSLContext(ssl.PROTOCOL_TLS_SERVER)
+
+    # We use str(pathlib.Path) here because PyPy doesn't accept Path objects.
+    # TODO: This is a bug in PyPy and should be reported to them, but their
+    # GitLab instance was offline when we found this bug. :'(
     ctx.load_cert_chain(
-        certfile=mkcert_certs.cert_file,
-        keyfile=mkcert_certs.key_file,
+        certfile=str(mkcert_certs.cert_file),
+        keyfile=str(mkcert_certs.key_file),
     )
 
     # we need keepalive_timeout=0