diff --git a/mco-gen/src/gen_impl.rs b/mco-gen/src/gen_impl.rs
index 58daa92..eb540e8 100644
--- a/mco-gen/src/gen_impl.rs
+++ b/mco-gen/src/gen_impl.rs
@@ -236,7 +236,7 @@ impl<A: Any> Gn<A> {
         Generator { gen }
     }
 
-    pub fn new_opt2<'a, T: Any, F>(size: usize, f: F,stack:Stack) -> Generator<'a, A, T>
+    pub fn new_opt_stack<'a, T: Any, F>( f: F,stack:Stack) -> Generator<'a, A, T>
         where
             F: FnOnce() -> T + Send + 'a,
     {
diff --git a/src/coroutine_impl.rs b/src/coroutine_impl.rs
index 879e859..99ec320 100644
--- a/src/coroutine_impl.rs
+++ b/src/coroutine_impl.rs
@@ -324,7 +324,7 @@ impl Builder {
 
         let mut co = CoroutineImpl {
             worker_thread_id: None,
-            inner: Gn::new_opt2(stack_size, closure, Stack::new(2048)),
+            inner: Gn::new_opt_stack(closure, Stack::new(2048)),
             reduce: None,
         };