diff --git a/apptools/persistence/tests/test_state_pickler.py b/apptools/persistence/tests/test_state_pickler.py
index 8d12935e3..a62b553f4 100644
--- a/apptools/persistence/tests/test_state_pickler.py
+++ b/apptools/persistence/tests/test_state_pickler.py
@@ -157,9 +157,8 @@ def verify(self, obj, state):
         self._check_instance_and_references(obj, data)
 
         num_attr = "numeric" if data["numeric"]["type"] == "numeric" else "ref"
-        decodestring = getattr(base64, "decodebytes", base64.decodestring)
         junk = state_pickler.gunzip_string(
-            decodestring(data[num_attr]["data"])
+            base64.decodebytes(data[num_attr]["data"])
         )
         num = pickle.loads(junk)
         self.assertEqual(numpy.alltrue(numpy.ravel(num == obj.numeric)), 1)
diff --git a/docs/releases/upcoming/210.test.rst b/docs/releases/upcoming/210.test.rst
new file mode 100644
index 000000000..867cb2111
--- /dev/null
+++ b/docs/releases/upcoming/210.test.rst
@@ -0,0 +1 @@
+Fix AttributeError on Python 3.9 due to usage of ``base64.decodestring`` in tests (#210)
\ No newline at end of file