diff --git a/exercises/simple-cipher/simple-cipher.spec.js b/exercises/simple-cipher/simple-cipher.spec.js
index 2f27067a17..745da6503b 100644
--- a/exercises/simple-cipher/simple-cipher.spec.js
+++ b/exercises/simple-cipher/simple-cipher.spec.js
@@ -45,6 +45,12 @@ describe('Incorrect key cipher', () => {
     }).toThrow(new Error('Bad key'));
   });
 
+  xtest('throws an error with a mixed-case key', () => {
+    expect(() => {
+      new Cipher('ABcdEF');
+    }).toThrow(new Error('Bad key'));
+  });
+
   xtest('throws an error with a numeric key', () => {
     expect(() => {
       new Cipher('12345');