diff --git a/exercises/practice/isbn-verifier/.meta/tests.toml b/exercises/practice/isbn-verifier/.meta/tests.toml
index 6d5a84599..722fffaed 100644
--- a/exercises/practice/isbn-verifier/.meta/tests.toml
+++ b/exercises/practice/isbn-verifier/.meta/tests.toml
@@ -30,6 +30,9 @@ description = "invalid character in isbn is not treated as zero"
 [28025280-2c39-4092-9719-f3234b89c627]
 description = "X is only valid as a check digit"
 
+[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/test/isbn_verifier_test.clj b/exercises/practice/isbn-verifier/test/isbn_verifier_test.clj
index df2cf6cc5..fc54b2d39 100644
--- a/exercises/practice/isbn-verifier/test/isbn_verifier_test.clj
+++ b/exercises/practice/isbn-verifier/test/isbn_verifier_test.clj
@@ -31,49 +31,53 @@
     (is (false? (isbn-verifier/isbn? "3-598-2X507-9")))))
 
 (deftest isbn?_test_8
+  (testing "X is not substituted by the value 10"
+    (is (false? (isbn-verifier/isbn? "3-598-2X507-5")))))
+
+(deftest isbn?_test_9
   (testing "valid isbn without separating dashes"
     (is (true? (isbn-verifier/isbn? "3598215088")))))
 
-(deftest isbn?_test_9
+(deftest isbn?_test_10
   (testing "isbn without separating dashes and X as check digit"
     (is (true? (isbn-verifier/isbn? "359821507X")))))
 
-(deftest isbn?_test_10
+(deftest isbn?_test_11
   (testing "isbn without check digit and dashes"
     (is (false? (isbn-verifier/isbn? "359821507")))))
 
-(deftest isbn?_test_11
+(deftest isbn?_test_12
   (testing "too long isbn and no dashes"
     (is (false? (isbn-verifier/isbn? "3598215078X")))))
 
-(deftest isbn?_test_12
+(deftest isbn?_test_13
   (testing "too short isbn"
     (is (false? (isbn-verifier/isbn? "00")))))
 
-(deftest isbn?_test_13
+(deftest isbn?_test_14
   (testing "isbn without check digit"
     (is (false? (isbn-verifier/isbn? "3-598-21507")))))
 
-(deftest isbn?_test_14
+(deftest isbn?_test_15
   (testing "check digit of X should not be used for 0"
     (is (false? (isbn-verifier/isbn? "3-598-21515-X")))))
 
-(deftest isbn?_test_15
+(deftest isbn?_test_16
   (testing "empty isbn"
     (is (false? (isbn-verifier/isbn? "")))))
 
-(deftest isbn?_test_16
+(deftest isbn?_test_17
   (testing "input is 9 characters"
     (is (false? (isbn-verifier/isbn? "134456729")))))
 
-(deftest isbn?_test_17
+(deftest isbn?_test_18
   (testing "invalid characters are not ignored after checking length"
     (is (false? (isbn-verifier/isbn? "3132P34035")))))
 
-(deftest isbn?_test_18
+(deftest isbn?_test_19
   (testing "invalid characters are not ignored before checking length"
     (is (false? (isbn-verifier/isbn? "3598P215088")))))
 
-(deftest isbn?_test_19
+(deftest isbn?_test_20
   (testing "input is too long but contains a valid isbn"
     (is (false? (isbn-verifier/isbn? "98245726788")))))