diff --git a/data_safe_haven/functions/typer_validators.py b/data_safe_haven/functions/typer_validators.py
index df72cd149c..91434740d9 100644
--- a/data_safe_haven/functions/typer_validators.py
+++ b/data_safe_haven/functions/typer_validators.py
@@ -13,7 +13,13 @@
 
 
 def typer_validator_factory(validator: Callable[[Any], Any]) -> Callable[[Any], Any]:
+    """Factory to create validation functions for Typer from Pydantic validators"""
     def typer_validator(x: Any) -> Any:
+        # Return unused optional arguments
+        if x is None:
+            return x
+
+        # Validate input, catching ValueError to raise Typer Exception
         try:
             validator(x)
             return x
diff --git a/tests_/functions/test_typer_validators.py b/tests_/functions/test_typer_validators.py
index 0c9c02ff90..72ae8b3f53 100644
--- a/tests_/functions/test_typer_validators.py
+++ b/tests_/functions/test_typer_validators.py
@@ -26,3 +26,6 @@ def test_typer_validate_aad_guid_fail(self, guid):
         with pytest.raises(BadParameter) as exc:
             typer_validate_aad_guid(guid)
             assert "Expected GUID" in exc
+
+    def test_typer_validate_aad_guid_nonae(self):
+        assert typer_validate_aad_guid(None) is None