diff --git a/decrypt_oracle/tox.ini b/decrypt_oracle/tox.ini
index 60aea91c7..f0a7804e5 100644
--- a/decrypt_oracle/tox.ini
+++ b/decrypt_oracle/tox.ini
@@ -156,6 +156,7 @@ basepython = python3
 deps =
     flake8
     flake8-docstrings
+    pydocstyle<4.0.0
     # https://github.com/JBKahn/flake8-print/pull/30
     flake8-print>=3.1.0
 commands =
diff --git a/src/aws_encryption_sdk/materials_managers/caching.py b/src/aws_encryption_sdk/materials_managers/caching.py
index b2bdcba9f..992a39a7a 100644
--- a/src/aws_encryption_sdk/materials_managers/caching.py
+++ b/src/aws_encryption_sdk/materials_managers/caching.py
@@ -108,6 +108,9 @@ def __attrs_post_init__(self):
         if self.max_bytes_encrypted > MAX_BYTES_PER_KEY:
             raise ValueError("max_bytes_encrypted cannot exceed {}".format(MAX_BYTES_PER_KEY))
 
+        if self.max_age <= 0.0:
+            raise ValueError("max_age cannot be less than or equal to 0")
+
         if self.backing_materials_manager is None:
             if self.master_key_provider is None:
                 raise TypeError("Either backing_materials_manager or master_key_provider must be defined")
diff --git a/test/unit/test_material_managers_caching.py b/test/unit/test_material_managers_caching.py
index 426fe3348..833d6aa53 100644
--- a/test/unit/test_material_managers_caching.py
+++ b/test/unit/test_material_managers_caching.py
@@ -117,6 +117,8 @@ def test_mkp_to_default_cmm(mocker):
             dict(max_bytes_encrypted=MAX_BYTES_PER_KEY + 1),
             r"max_bytes_encrypted cannot exceed {}".format(MAX_BYTES_PER_KEY),
         ),
+        (dict(max_age=0.0), r"max_age cannot be less than or equal to 0"),
+        (dict(max_age=-1.0), r"max_age cannot be less than or equal to 0"),
     ),
 )
 def test_invalid_values(invalid_kwargs, error_message):
diff --git a/tox.ini b/tox.ini
index e13ea2cb8..06564ef6a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -117,6 +117,7 @@ basepython = python3
 deps =
     flake8
     flake8-docstrings
+    pydocstyle<4.0.0
     # https://github.com/JBKahn/flake8-print/pull/30
     flake8-print>=3.1.0
     flake8-bugbear