diff --git a/examples/circom_full_flow.rs b/examples/circom_full_flow.rs
index dccf0d8..31755c7 100644
--- a/examples/circom_full_flow.rs
+++ b/examples/circom_full_flow.rs
@@ -84,6 +84,7 @@ fn main() {
     // prepare the Nova prover & verifier params
     let nova_preprocess_params = PreprocessorParam::new(poseidon_config, f_circuit.clone());
     let nova_params = N::preprocess(&mut rng, &nova_preprocess_params).unwrap();
+    let pp_hash = nova_params.1.pp_hash().unwrap();
 
     // initialize the folding scheme engine, in our case we use Nova
     let mut nova = N::init(&nova_params, f_circuit.clone(), z_0).unwrap();
@@ -131,6 +132,7 @@ fn main() {
 
     let calldata: Vec<u8> = prepare_calldata(
         function_selector,
+        pp_hash,
         nova.i,
         nova.z_0,
         nova.z_i,
diff --git a/examples/full_flow.rs b/examples/full_flow.rs
index bf1f28f..7b586ea 100644
--- a/examples/full_flow.rs
+++ b/examples/full_flow.rs
@@ -101,6 +101,7 @@ fn main() {
     // prepare the Nova prover & verifier params
     let nova_preprocess_params = PreprocessorParam::new(poseidon_config.clone(), f_circuit);
     let nova_params = N::preprocess(&mut rng, &nova_preprocess_params).unwrap();
+    let pp_hash = nova_params.1.pp_hash().unwrap();
 
     // initialize the folding scheme engine, in our case we use Nova
     let mut nova = N::init(&nova_params, f_circuit, z_0).unwrap();
@@ -138,6 +139,7 @@ fn main() {
 
     let calldata: Vec<u8> = prepare_calldata(
         function_selector,
+        pp_hash,
         nova.i,
         nova.z_0,
         nova.z_i,
diff --git a/examples/noir_full_flow.rs b/examples/noir_full_flow.rs
index 6453109..30f2e89 100644
--- a/examples/noir_full_flow.rs
+++ b/examples/noir_full_flow.rs
@@ -74,6 +74,7 @@ fn main() {
     // prepare the Nova prover & verifier params
     let nova_preprocess_params = PreprocessorParam::new(poseidon_config, f_circuit.clone());
     let nova_params = N::preprocess(&mut rng, &nova_preprocess_params).unwrap();
+    let pp_hash = nova_params.1.pp_hash().unwrap();
 
     // initialize the folding scheme engine, in our case we use Nova
     let mut nova = N::init(&nova_params, f_circuit.clone(), z_0).unwrap();
@@ -119,6 +120,7 @@ fn main() {
 
     let calldata: Vec<u8> = prepare_calldata(
         function_selector,
+        pp_hash,
         nova.i,
         nova.z_0,
         nova.z_i,
diff --git a/examples/noname_full_flow.rs b/examples/noname_full_flow.rs
index 00dccbf..0a6c0d4 100644
--- a/examples/noname_full_flow.rs
+++ b/examples/noname_full_flow.rs
@@ -84,6 +84,7 @@ fn main() {
     // prepare the Nova prover & verifier params
     let nova_preprocess_params = PreprocessorParam::new(poseidon_config, f_circuit.clone());
     let nova_params = N::preprocess(&mut rng, &nova_preprocess_params).unwrap();
+    let pp_hash = nova_params.1.pp_hash().unwrap();
 
     // initialize the folding scheme engine, in our case we use Nova
     let mut nova = N::init(&nova_params, f_circuit.clone(), z_0).unwrap();
@@ -131,6 +132,7 @@ fn main() {
 
     let calldata: Vec<u8> = prepare_calldata(
         function_selector,
+        pp_hash,
         nova.i,
         nova.z_0,
         nova.z_i,
diff --git a/folding-schemes/src/folding/nova/decider_eth.rs b/folding-schemes/src/folding/nova/decider_eth.rs
index 4e4719e..d17b3fe 100644
--- a/folding-schemes/src/folding/nova/decider_eth.rs
+++ b/folding-schemes/src/folding/nova/decider_eth.rs
@@ -25,6 +25,7 @@ use crate::commitment::{
     CommitmentScheme,
 };
 use crate::folding::circuits::{nonnative::affine::NonNativeAffineVar, CF2};
+use crate::folding::nova::circuits::ChallengeGadget;
 use crate::frontend::FCircuit;
 use crate::transcript::poseidon::poseidon_canonical_config;
 use crate::Error;
@@ -277,14 +278,30 @@ where
 #[allow(clippy::too_many_arguments)]
 pub fn prepare_calldata(
     function_signature_check: [u8; 4],
+    pp_hash: ark_bn254::Fr,
     i: ark_bn254::Fr,
     z_0: Vec<ark_bn254::Fr>,
     z_i: Vec<ark_bn254::Fr>,
-    r: ark_bn254::Fr,
     running_instance: &CommittedInstance<ark_bn254::G1Projective>,
     incoming_instance: &CommittedInstance<ark_bn254::G1Projective>,
     proof: Proof<ark_bn254::G1Projective, KZG<'static, Bn254>, Groth16<Bn254>>,
 ) -> Result<Vec<u8>, Error> {
+    // compute the challenge r
+    let poseidon_config = poseidon_canonical_config::<ark_bn254::Fr>();
+    let mut transcript = PoseidonSponge::<ark_bn254::Fr>::new(&poseidon_config);
+    let r_bits = ChallengeGadget::<
+        ark_bn254::G1Projective,
+        CommittedInstance<ark_bn254::G1Projective>,
+    >::get_challenge_native(
+        &mut transcript,
+        pp_hash,
+        running_instance,
+        incoming_instance,
+        Some(&proof.cmT),
+    );
+    let r =
+        ark_bn254::Fr::from_bigint(BigInteger::from_bits_le(&r_bits)).ok_or(Error::OutOfBounds)?;
+
     Ok(vec![
         function_signature_check.to_vec(),
         i.into_bigint().to_bytes_be(), // i