diff --git a/vm/src/builtins/union.rs b/vm/src/builtins/union.rs
index 970144d4a..1c43eab7b 100644
--- a/vm/src/builtins/union.rs
+++ b/vm/src/builtins/union.rs
@@ -198,7 +198,7 @@ fn dedup_and_flatten_args(args: PyTupleRef, vm: &VirtualMachine) -> PyTupleRef {
         if !new_args.iter().any(|param| {
             param
                 .rich_compare_bool(arg, PyComparisonOp::Eq, vm)
-                .unwrap()
+                .expect("types are always comparable")
         }) {
             new_args.push(arg.clone());
         }