diff --git a/exercises/traits/traits4.rs b/exercises/traits/traits4.rs
index 6b541665..86f8e933 100644
--- a/exercises/traits/traits4.rs
+++ b/exercises/traits/traits4.rs
@@ -33,7 +33,7 @@ mod tests {
         let some_software = SomeSoftware {};
         let other_software = OtherSoftware {};
 
-        assert!(compare_license_types(some_software, other_software));
+        assert!(compare_license_types(&some_software, &other_software));
     }
 
     #[test]
@@ -41,6 +41,6 @@ mod tests {
         let some_software = SomeSoftware {};
         let other_software = OtherSoftware {};
 
-        assert!(compare_license_types(other_software, some_software));
+        assert!(compare_license_types(&other_software, &some_software));
     }
 }