diff --git a/vm/src/obj/objbytes.rs b/vm/src/obj/objbytes.rs
index 190fdd061d..db561e4355 100644
--- a/vm/src/obj/objbytes.rs
+++ b/vm/src/obj/objbytes.rs
@@ -1,4 +1,5 @@
 use std::cell::Cell;
+use std::mem::size_of;
 use std::ops::Deref;
 
 use wtf8;
@@ -149,6 +150,11 @@ impl PyBytesRef {
         }
     }
 
+    #[pymethod(name = "__sizeof__")]
+    fn sizeof(self, _vm: &VirtualMachine) -> PyResult<usize> {
+        Ok(size_of::<Self>() + self.inner.elements.len() * size_of::<u8>())
+    }
+
     #[pymethod(name = "__add__")]
     fn add(self, other: PyObjectRef, vm: &VirtualMachine) -> PyResult {
         if let Ok(other) = PyByteInner::try_from_object(vm, other) {