diff --git a/benches/swap.rs b/benches/swap.rs
index f072ff5..6e7c832 100644
--- a/benches/swap.rs
+++ b/benches/swap.rs
@@ -10,7 +10,7 @@ static mut ctx_slot: *mut Context<'static, lwkt::os::Stack> = 0 as *mut Context<
 #[bench]
 fn swap(b: &mut test::Bencher) {
   unsafe {
-    let stack = lwkt::os::StackSource::get_stack(4 << 20).unwrap();
+    let stack = lwkt::os::StackSource.get_stack(4 << 20).unwrap();
 
     let mut ctx = Context::new(stack, move || {
       let ctx_ptr = ctx_slot;
diff --git a/examples/basic.rs b/examples/basic.rs
index f61f3d2..791eafd 100644
--- a/examples/basic.rs
+++ b/examples/basic.rs
@@ -7,7 +7,7 @@ static mut ctx_slot: *mut Context<'static, lwkt::os::Stack> = 0 as *mut Context<
 
 fn main() {
   unsafe {
-    let stack = lwkt::os::StackSource::get_stack(4 << 20).unwrap();
+    let stack = lwkt::os::StackSource.get_stack(4 << 20).unwrap();
 
     let mut ctx = Context::new(stack, move || {
       println!("it's alive!");
diff --git a/src/os/mod.rs b/src/os/mod.rs
index 0ae1537..fcf24f2 100644
--- a/src/os/mod.rs
+++ b/src/os/mod.rs
@@ -30,7 +30,7 @@ impl stack::StackSource for StackSource {
   type Output = Stack;
   type Error = IoError;
 
-  fn get_stack(size: usize) -> Result<Stack, IoError> {
+  fn get_stack(&mut self, size: usize) -> Result<Stack, IoError> {
     let page_size = sys::page_size();
 
     // round the page size up,
diff --git a/src/stack.rs b/src/stack.rs
index 2fb06df..60b0c3b 100644
--- a/src/stack.rs
+++ b/src/stack.rs
@@ -20,5 +20,5 @@ pub trait Stack {
 pub trait StackSource {
   type Output: Stack;
   type Error: Debug + Display = ();
-  fn get_stack(size: usize) -> Result<Self::Output, Self::Error>;
+  fn get_stack(&mut self, size: usize) -> Result<Self::Output, Self::Error>;
 }