diff --git a/vm/src/obj/objbuiltinfunc.rs b/vm/src/obj/objbuiltinfunc.rs
index 928f240b0..6d198156a 100644
--- a/vm/src/obj/objbuiltinfunc.rs
+++ b/vm/src/obj/objbuiltinfunc.rs
@@ -6,8 +6,7 @@ use crate::pyobject::PyValue;
 use crate::vm::VirtualMachine;
 
 pub struct PyBuiltinFunction {
-    // TODO: shouldn't be public
-    pub value: PyNativeFunc,
+    value: PyNativeFunc,
 }
 
 impl PyValue for PyBuiltinFunction {
@@ -26,4 +25,8 @@ impl PyBuiltinFunction {
     pub fn new(value: PyNativeFunc) -> Self {
         Self { value }
     }
+
+    pub fn as_func(&self) -> &PyNativeFunc {
+        &self.value
+    }
 }
diff --git a/vm/src/vm.rs b/vm/src/vm.rs
index 918d52060..d82f224fd 100644
--- a/vm/src/vm.rs
+++ b/vm/src/vm.rs
@@ -673,8 +673,8 @@ impl VirtualMachine {
                 args
             };
             self.invoke(&function, args)
-        } else if let Some(PyBuiltinFunction { ref value }) = func_ref.payload() {
-            value(self, args)
+        } else if let Some(builtin_func) = func_ref.payload::<PyBuiltinFunction>() {
+            builtin_func.as_func()(self, args)
         } else if self.is_callable(&func_ref) {
             self.call_method(&func_ref, "__call__", args)
         } else {