diff --git a/exercises/practice/isbn-verifier/.meta/tests.toml b/exercises/practice/isbn-verifier/.meta/tests.toml
index 6d5a8459..17e18d47 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_tests.plt b/exercises/practice/isbn-verifier/isbn_verifier_tests.plt
index 1208eb5c..45ccbabb 100644
--- a/exercises/practice/isbn-verifier/isbn_verifier_tests.plt
+++ b/exercises/practice/isbn-verifier/isbn_verifier_tests.plt
@@ -27,6 +27,12 @@ pending :-
     test(x_is_only_valid_as_a_check_digit, [fail, condition(pending)]) :-
         isbn("3-598-2X507-9").
 
+    test(only_one_check_digit_is_allowed, [fail, condition(pending)]) :-
+        isbn("3-598-21508-96").
+
+    test(x_is_not_substituted_by_the_value_10, [fail, condition(pending)]) :-
+        isbn("3-598-2X507-5").
+
     test(valid_isbn_without_separating_dashes, condition(pending)) :-
         isbn("3598215088").