diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 442ca15..0eab69d 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -13,7 +13,7 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu-latest ]
-        python-version: [ "3.11" ]
+        python-version: [ "3.11", "3.9" ]
         pydantic: [ "pydantic1", "pydantic2" ]
     steps:
       - uses: actions/checkout@v2
diff --git a/pyproject.toml b/pyproject.toml
index 81f98f9..b221004 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -7,7 +7,7 @@ name = "semra"
 dynamic = ["version"]
 description = 'Semantic Mapping Reasoning Assembler'
 readme = "README.md"
-requires-python = ">=3.10"
+requires-python = ">=3.9"
 license = "MIT"
 keywords = []
 authors = [
@@ -16,6 +16,7 @@ authors = [
 classifiers = [
   "Development Status :: 4 - Beta",
   "Programming Language :: Python",
+  "Programming Language :: Python :: 3.9",
   "Programming Language :: Python :: 3.10",
   "Programming Language :: Python :: 3.11",
   "Programming Language :: Python :: Implementation :: CPython",
@@ -31,6 +32,7 @@ dependencies = [
   "bioregistry",
   "bioontologies",
   "pyobo",
+  "typing_extensions",
 ]
 
 [project.optional-dependencies]
@@ -74,7 +76,7 @@ cov = [
 ]
 
 [[tool.hatch.envs.all.matrix]]
-python = ["3.10", "3.11"]
+python = ["3.9", "3.11"]
 
 [tool.hatch.envs.lint]
 detached = true
@@ -100,11 +102,11 @@ all = [
 ]
 
 [tool.black]
-target-version = ["py311"]
+target-version = ["py39"]
 line-length = 120
 
 [tool.ruff]
-target-version = "py311"
+target-version = "py39"
 line-length = 120
 select = [
   "A",
diff --git a/src/semra/client.py b/src/semra/client.py
index 556cdf4..badfde0 100644
--- a/src/semra/client.py
+++ b/src/semra/client.py
@@ -5,7 +5,7 @@
 import os
 import typing as t
 from collections import Counter
-from typing import Any, TypeAlias
+from typing import Any
 
 import bioregistry
 import neo4j
@@ -13,6 +13,7 @@
 import networkx as nx
 import pydantic
 from neo4j import Transaction, unit_of_work
+from typing_extensions import TypeAlias
 
 import semra
 from semra import Evidence, MappingSet, Reference
@@ -25,9 +26,9 @@
 
 Node: TypeAlias = t.Mapping[str, Any]
 
-TxResult: TypeAlias = list[list[Any]] | None
+TxResult: TypeAlias = t.Optional[list[list[Any]]]
 
-ReferenceHint: TypeAlias = str | Reference
+ReferenceHint: TypeAlias = t.Union[str, Reference]
 
 
 class Neo4jClient: