diff --git a/src/rcore.rs b/src/rcore.rs
index ceb224c..b59bc89 100644
--- a/src/rcore.rs
+++ b/src/rcore.rs
@@ -69,6 +69,8 @@ pub struct DeCtxT<'a: 'c, 'c, Ctx: Context<'a>> {
 pub trait DeCtx<'a, Ctx: Context<'a>> {
     fn deserializer(&mut self) -> &mut dyn Deserializer;
 
+    fn tell(&self) -> usize;
+
     fn next_address(&mut self) -> Result<Address, &[u8]>;
 
     fn resolver(&self) -> Rc<dyn Resolver<'a, Ctx>>;
@@ -87,6 +89,10 @@ impl<'a: 'c, 'c, Ctx: Context<'a>> DeCtx<'a, Ctx> for DeCtxT<'a, 'c, Ctx> {
         self.deserializer
     }
 
+    fn tell(&self) -> usize {
+        self.deserializer.tell()
+    }
+
     fn next_address(&mut self) -> Result<Address, &[u8]> {
         self.addresses.next(self.deserializer)
     }