diff --git a/exercises/practice/isbn-verifier/.meta/tests.toml b/exercises/practice/isbn-verifier/.meta/tests.toml
index 6d5a845990..17e18d47ac 100644
--- a/exercises/practice/isbn-verifier/.meta/tests.toml
+++ b/exercises/practice/isbn-verifier/.meta/tests.toml
@@ -30,6 +30,12 @@ description = "invalid character in isbn is not treated as zero"
 [28025280-2c39-4092-9719-f3234b89c627]
 description = "X is only valid as a check digit"
 
+[8005b57f-f194-44ee-88d2-a77ac4142591]
+description = "only one check digit is allowed"
+
+[fdb14c99-4cf8-43c5-b06d-eb1638eff343]
+description = "X is not substituted by the value 10"
+
 [f6294e61-7e79-46b3-977b-f48789a4945b]
 description = "valid isbn without separating dashes"
 
diff --git a/exercises/practice/isbn-verifier/isbn_verifier_test.py b/exercises/practice/isbn-verifier/isbn_verifier_test.py
index dbcddf19d4..5c9bf6f755 100644
--- a/exercises/practice/isbn-verifier/isbn_verifier_test.py
+++ b/exercises/practice/isbn-verifier/isbn_verifier_test.py
@@ -1,6 +1,6 @@
 # These tests are auto-generated with test data from:
 # https://github.com/exercism/problem-specifications/tree/main/exercises/isbn-verifier/canonical-data.json
-# File last updated on 2023-07-19
+# File last updated on 2025-12-30
 
 import unittest
 
@@ -31,6 +31,12 @@ def test_invalid_character_in_isbn_is_not_treated_as_zero(self):
     def test_x_is_only_valid_as_a_check_digit(self):
         self.assertIs(is_valid("3-598-2X507-9"), False)
 
+    def test_only_one_check_digit_is_allowed(self):
+        self.assertIs(is_valid("3-598-21508-96"), False)
+
+    def test_x_is_not_substituted_by_the_value_10(self):
+        self.assertIs(is_valid("3-598-2X507-5"), False)
+
     def test_valid_isbn_without_separating_dashes(self):
         self.assertIs(is_valid("3598215088"), True)