diff --git a/exercises/03_ticket_v1/10_references_in_memory/src/lib.rs b/exercises/03_ticket_v1/10_references_in_memory/src/lib.rs
index 7305514..d580758 100644
--- a/exercises/03_ticket_v1/10_references_in_memory/src/lib.rs
+++ b/exercises/03_ticket_v1/10_references_in_memory/src/lib.rs
@@ -18,7 +18,7 @@ mod tests {
 
     #[test]
     fn u64_mut_ref_size() {
-        assert_eq!(size_of::<&u64>(), todo!());
+        assert_eq!(size_of::<&mut u64>(), todo!());
     }
 
     #[test]