diff --git a/luhn.py b/luhn.py
index 1136808..6d20498 100644
--- a/luhn.py
+++ b/luhn.py
@@ -16,7 +16,8 @@ def _digits(value: NumberLike) -> str:
 
     if not cleaned or not cleaned.isdigit():
         raise ValueError(
-            "value must contain digits only, with optional spaces or hyphens"
+            "value must contain digits only, with optional spaces, hyphens, "
+            "dots, slashes, backslashes, or commas"
         )
 
     return cleaned
diff --git a/test_luhn.py b/test_luhn.py
index 2b32579..add2f7b 100644
--- a/test_luhn.py
+++ b/test_luhn.py
@@ -30,7 +30,12 @@ def test_append_check_digit(self):
         self.assertEqual(append_check_digit("7992739871"), "79927398713")
 
     def test_rejects_non_digit_payloads(self):
-        with self.assertRaises(ValueError):
+        expected_message = (
+            "value must contain digits only, with optional spaces, hyphens, "
+            "dots, slashes, backslashes, or commas"
+        )
+
+        with self.assertRaisesRegex(ValueError, expected_message):
             calculate_check_digit("123x")
 
     def test_rejects_unsupported_types(self):