diff --git a/questions/645-medium-diff/test-cases.ts b/questions/645-medium-diff/test-cases.ts
index 40575bdc..48dda07d 100644
--- a/questions/645-medium-diff/test-cases.ts
+++ b/questions/645-medium-diff/test-cases.ts
@@ -11,5 +11,6 @@ type Bar = {
 }
 
 type cases = [
-  Expect<Equal<Diff<Foo, Bar>, { gender: number }>>
+  Expect<Equal<Diff<Foo, Bar>, { gender: number }>>,
+  Expect<Equal<Diff<Bar,Foo>, { gender: number }>>
 ]