diff --git a/tests/unit_server/arghandler_test.py b/tests/unit_server/arghandler_test.py
index 73512349..96bce31a 100644
--- a/tests/unit_server/arghandler_test.py
+++ b/tests/unit_server/arghandler_test.py
@@ -540,15 +540,21 @@ def test_220__argparse_nargs(argument_source: str) -> None:
     test_130__duplicates(argument_source)
 
 
+class MyError(Exception):
+    """Used below."""
+
+
 @pytest.mark.parametrize(
     "argument_source",
     [QUERY_ARGUMENTS, JSON_BODY_ARGUMENTS],
 )
 @pytest.mark.parametrize(
     "exc",
-    [TypeError, ValueError, argparse.ArgumentTypeError, argparse.ArgumentError],
+    [TypeError, ValueError, argparse.ArgumentError, RuntimeError, IndexError, MyError],
 )
-def test_230__argparse_catch_most__error(argument_source: str, exc: Exception) -> None:
+def test_230__argparse_custom_validation__error(
+    argument_source: str, exc: Exception
+) -> None:
     """Test `argument_source` arguments using argparse's advanced options."""
     args: Dict[str, Any] = {
         "foo": "True",
@@ -574,11 +580,53 @@ def _error_it(_: Any, exc: Exception):
             arg,
             type=lambda x: _error_it(
                 x,
-                exc("it's a bad value"),  # type: ignore
+                exc("it's a bad value but you won't see this message anyway..."),  # type: ignore
             ),
         )
 
     with pytest.raises(tornado.web.HTTPError) as e:
         arghand.parse_args()
 
-    assert str(e.value) == "HTTP 400: argument foo: it's a bad value"
+    assert str(e.value) == "HTTP 400: argument foo: invalid type"
+
+
+@pytest.mark.parametrize(
+    "argument_source",
+    [QUERY_ARGUMENTS, JSON_BODY_ARGUMENTS],
+)
+def test_235__argparse_custom_validation__argumenttypeerror__error(
+    argument_source: str,
+) -> None:
+    """Test `argument_source` arguments using argparse's advanced options."""
+    args: Dict[str, Any] = {
+        "foo": "True",
+    }
+    if argument_source == JSON_BODY_ARGUMENTS:
+        args = {
+            "foo": [1, 2, 3],
+        }
+
+    # set up ArgumentHandler
+    arghand = setup_argument_handler(
+        argument_source,
+        args,
+    )
+
+    def _error_it():
+        raise argparse.ArgumentTypeError("it's a bad value and you *will* see this!")
+
+    for arg, _ in args.items():
+        print()
+        print(arg)
+        arghand.add_argument(
+            arg,
+            type=_error_it,
+        )
+
+    with pytest.raises(tornado.web.HTTPError) as e:
+        arghand.parse_args()
+
+    assert (
+        str(e.value)
+        == "HTTP 400: argument foo: it's a bad value and you *will* see this!"
+    )