diff --git a/vm/src/builtins/genericalias.rs b/vm/src/builtins/genericalias.rs
index b91e41a97..233e746e0 100644
--- a/vm/src/builtins/genericalias.rs
+++ b/vm/src/builtins/genericalias.rs
@@ -209,27 +209,33 @@ fn subs_tvars(
     argitems: &[PyObjectRef],
     vm: &VirtualMachine,
 ) -> PyResult {
-    obj.clone_class()
-        .get_attr("__parameters__")
+    obj.clone()
+        .get_attr("__parameters__", vm)
+        .ok()
         .and_then(|sub_params| {
             PyTupleRef::try_from_object(vm, sub_params)
                 .ok()
                 .map(|sub_params| {
-                    let sub_args = sub_params
-                        .as_slice()
-                        .iter()
-                        .map(|arg| {
-                            if let Some(idx) = tuple_index(params, arg) {
-                                argitems[idx].clone()
-                            } else {
-                                arg.clone()
-                            }
-                        })
-                        .collect::<Vec<_>>();
-                    let sub_args: PyObjectRef = PyTuple::new_ref(sub_args, &vm.ctx).into();
-                    obj.get_item(sub_args, vm)
+                    if sub_params.len() > 0 {
+                        let sub_args = sub_params
+                            .as_slice()
+                            .iter()
+                            .map(|arg| {
+                                if let Some(idx) = tuple_index(params, arg) {
+                                    argitems[idx].clone()
+                                } else {
+                                    arg.clone()
+                                }
+                            })
+                            .collect::<Vec<_>>();
+                        let sub_args: PyObjectRef = PyTuple::new_ref(sub_args, &vm.ctx).into();
+                        Some(obj.get_item(sub_args, vm))
+                    } else {
+                        None
+                    }
                 })
         })
+        .flatten()
         .unwrap_or(Ok(obj))
 }