diff --git a/vm/src/protocol/buffer.rs b/vm/src/protocol/buffer.rs
index 48985330a2..4af99b032d 100644
--- a/vm/src/protocol/buffer.rs
+++ b/vm/src/protocol/buffer.rs
@@ -108,7 +108,7 @@ impl TryFromBorrowedObject for PyBuffer {
         let obj_cls = obj.class();
         for cls in obj_cls.iter_mro() {
             if let Some(f) = cls.slots.as_buffer.as_ref() {
-                return f(obj, vm);
+                return obj.with_ptr(|obj| f(obj, vm));
             }
         }
         Err(vm.new_type_error(format!(
diff --git a/vm/src/types/slot.rs b/vm/src/types/slot.rs
index f638615060..18bfb3ffe3 100644
--- a/vm/src/types/slot.rs
+++ b/vm/src/types/slot.rs
@@ -134,7 +134,7 @@ pub(crate) type HashFunc = fn(PyObjectPtr, &VirtualMachine) -> PyResult<PyHash>;
 pub(crate) type GetattroFunc = fn(PyObjectRef, PyStrRef, &VirtualMachine) -> PyResult;
 pub(crate) type SetattroFunc =
     fn(&PyObjectRef, PyStrRef, Option<PyObjectRef>, &VirtualMachine) -> PyResult<()>;
-pub(crate) type AsBufferFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<PyBuffer>;
+pub(crate) type AsBufferFunc = fn(PyObjectPtr, &VirtualMachine) -> PyResult<PyBuffer>;
 pub(crate) type RichCompareFunc = fn(
     PyObjectPtr,
     PyObjectPtr,
@@ -754,7 +754,7 @@ pub trait AsBuffer: PyValue {
     // TODO: `flags` parameter
     #[inline]
     #[pyslot]
-    fn slot_as_buffer(zelf: &PyObjectRef, vm: &VirtualMachine) -> PyResult<PyBuffer> {
+    fn slot_as_buffer(zelf: PyObjectPtr, vm: &VirtualMachine) -> PyResult<PyBuffer> {
         let zelf = zelf
             .downcast_ref()
             .ok_or_else(|| vm.new_type_error("unexpected payload for as_buffer".to_owned()))?;