diff --git a/src/bin/bench_recursion.rs b/src/bin/bench_recursion.rs
index 9fab2456..1c9104f9 100644
--- a/src/bin/bench_recursion.rs
+++ b/src/bin/bench_recursion.rs
@@ -18,12 +18,6 @@ fn main() {
     env_logger::Builder::from_env(Env::default().default_filter_or("debug")).init();
 
     bench_prove::<CrandallField, 4>();
-
-    // bench_field_mul::<CrandallField>();
-
-    // bench_fft();
-    println!();
-    // bench_gmimc::<CrandallField>();
 }
 
 fn bench_prove<F: Field + Extendable<D>, const D: usize>() {
@@ -51,12 +45,6 @@ fn bench_prove<F: Field + Extendable<D>, const D: usize>() {
 
     builder.add_gate(ConstantGate::get(), vec![F::NEG_ONE]);
 
-    // for _ in 0..(40 * 5) {
-    //     builder.add_gate(
-    //         FriConsistencyGate::new(2, 3, 13),
-    //         vec![F::primitive_root_of_unity(13)]);
-    // }
-
     let prover = builder.build_prover();
     let inputs = PartialWitness::new();
     prover.prove(inputs);
diff --git a/src/circuit_builder.rs b/src/circuit_builder.rs
index 72c27208..1fe5a5e1 100644
--- a/src/circuit_builder.rs
+++ b/src/circuit_builder.rs
@@ -319,11 +319,12 @@ impl<F: Extendable<D>, const D: usize> CircuitBuilder<F, D> {
             sigmas_root,
         };
 
-        let generators = self.generators;
         let prover_only = ProverOnlyCircuitData {
-            generators,
+            generators: self.generators,
             constants_commitment,
             sigmas_commitment,
+            copy_constraints: self.copy_constraints,
+            gate_instances: self.gate_instances,
         };
 
         // The HashSet of gates will have a non-deterministic order. When converting to a Vec, we
diff --git a/src/circuit_data.rs b/src/circuit_data.rs
index fe4fd0e0..93fa06e5 100644
--- a/src/circuit_data.rs
+++ b/src/circuit_data.rs
@@ -3,11 +3,12 @@ use anyhow::Result;
 use crate::field::extension_field::Extendable;
 use crate::field::field::Field;
 use crate::fri::FriConfig;
-use crate::gates::gate::PrefixedGate;
+use crate::gates::gate::{GateInstance, PrefixedGate};
 use crate::generator::WitnessGenerator;
 use crate::polynomial::commitment::ListPolynomialCommitment;
 use crate::proof::{Hash, HashTarget, Proof};
 use crate::prover::prove;
+use crate::target::Target;
 use crate::verifier::verify;
 use crate::witness::PartialWitness;
 
@@ -67,7 +68,7 @@ impl CircuitConfig {
 
 /// Circuit data required by the prover or the verifier.
 pub struct CircuitData<F: Extendable<D>, const D: usize> {
-    pub(crate) prover_only: ProverOnlyCircuitData<F>,
+    pub(crate) prover_only: ProverOnlyCircuitData<F, D>,
     pub(crate) verifier_only: VerifierOnlyCircuitData<F>,
     pub(crate) common: CommonCircuitData<F, D>,
 }
@@ -90,7 +91,7 @@ impl<F: Extendable<D>, const D: usize> CircuitData<F, D> {
 /// required, like LDEs of preprocessed polynomials. If more succinctness was desired, we could
 /// construct a more minimal prover structure and convert back and forth.
 pub struct ProverCircuitData<F: Extendable<D>, const D: usize> {
-    pub(crate) prover_only: ProverOnlyCircuitData<F>,
+    pub(crate) prover_only: ProverOnlyCircuitData<F, D>,
     pub(crate) common: CommonCircuitData<F, D>,
 }
 
@@ -113,12 +114,16 @@ impl<F: Extendable<D>, const D: usize> VerifierCircuitData<F, D> {
 }
 
 /// Circuit data required by the prover, but not the verifier.
-pub(crate) struct ProverOnlyCircuitData<F: Field> {
+pub(crate) struct ProverOnlyCircuitData<F: Extendable<D>, const D: usize> {
     pub generators: Vec<Box<dyn WitnessGenerator<F>>>,
     /// Commitments to the constants polynomial.
     pub constants_commitment: ListPolynomialCommitment<F>,
     /// Commitments to the sigma polynomial.
     pub sigmas_commitment: ListPolynomialCommitment<F>,
+    /// The circuit's copy constraints.
+    pub copy_constraints: Vec<(Target, Target)>,
+    /// The concrete placement of each gate in the circuit.
+    pub gate_instances: Vec<GateInstance<F, D>>,
 }
 
 /// Circuit data required by the verifier, but not the prover.
diff --git a/src/field/fft.rs b/src/field/fft.rs
index 8bcde967..e1c1a097 100644
--- a/src/field/fft.rs
+++ b/src/field/fft.rs
@@ -126,32 +126,11 @@ pub(crate) fn fft_with_precomputation_power_of_2<F: Field>(
     PolynomialValues { values }
 }
 
-pub(crate) fn coset_fft<F: Field>(poly: PolynomialCoeffs<F>, shift: F) -> PolynomialValues<F> {
-    let mut points = fft(poly);
-    let mut shift_exp_i = F::ONE;
-    for p in points.values.iter_mut() {
-        *p *= shift_exp_i;
-        shift_exp_i *= shift;
-    }
-    points
-}
-
 pub(crate) fn ifft<F: Field>(poly: PolynomialValues<F>) -> PolynomialCoeffs<F> {
     let precomputation = fft_precompute(poly.len());
     ifft_with_precomputation_power_of_2(poly, &precomputation)
 }
 
-pub(crate) fn coset_ifft<F: Field>(poly: PolynomialValues<F>, shift: F) -> PolynomialCoeffs<F> {
-    let shift_inv = shift.inverse();
-    let mut shift_inv_exp_i = F::ONE;
-    let mut coeffs = ifft(poly);
-    for c in coeffs.coeffs.iter_mut() {
-        *c *= shift_inv_exp_i;
-        shift_inv_exp_i *= shift_inv;
-    }
-    coeffs
-}
-
 #[cfg(test)]
 mod tests {
     use crate::field::crandall_field::CrandallField;
diff --git a/src/gadgets/arithmetic.rs b/src/gadgets/arithmetic.rs
index 520f8cd9..7a9fd441 100644
--- a/src/gadgets/arithmetic.rs
+++ b/src/gadgets/arithmetic.rs
@@ -385,8 +385,6 @@ mod tests {
 
         let x = FF::rand();
         let y = FF::rand();
-        let x = FF::TWO;
-        let y = FF::ONE;
         let z = x / y;
         let xt = builder.constant_extension(x);
         let yt = builder.constant_extension(y);
diff --git a/src/gates/gmimc.rs b/src/gates/gmimc.rs
index 19042d57..bdfade7c 100644
--- a/src/gates/gmimc.rs
+++ b/src/gates/gmimc.rs
@@ -323,6 +323,8 @@ mod tests {
     use crate::gates::gmimc::{GMiMCGate, W};
     use crate::generator::generate_partial_witness;
     use crate::gmimc::gmimc_permute_naive;
+    use crate::permutation_argument::TargetPartitions;
+    use crate::target::Target;
     use crate::wire::Wire;
     use crate::witness::PartialWitness;
 
diff --git a/src/generator.rs b/src/generator.rs
index 443809b6..db81172f 100644
--- a/src/generator.rs
+++ b/src/generator.rs
@@ -2,6 +2,7 @@ use std::collections::{HashMap, HashSet};
 use std::fmt::Debug;
 
 use crate::field::field::Field;
+use crate::permutation_argument::TargetPartitions;
 use crate::target::Target;
 use crate::witness::PartialWitness;
 
@@ -24,10 +25,7 @@ pub(crate) fn generate_partial_witness<F: Field>(
 
     // Build a list of "pending" generators which are queued to be run. Initially, all generators
     // are queued.
-    let mut pending_generator_indices = HashSet::new();
-    for i in 0..generators.len() {
-        pending_generator_indices.insert(i);
-    }
+    let mut pending_generator_indices: HashSet<_> = (0..generators.len()).collect();
 
     // We also track a list of "expired" generators which have already returned false.
     let mut expired_generator_indices = HashSet::new();
@@ -58,6 +56,11 @@ pub(crate) fn generate_partial_witness<F: Field>(
 
         pending_generator_indices = next_pending_generator_indices;
     }
+    assert_eq!(
+        expired_generator_indices.len(),
+        generators.len(),
+        "Some generators weren't run."
+    );
 }
 
 /// A generator participates in the generation of the witness.
diff --git a/src/plonk_challenger.rs b/src/plonk_challenger.rs
index b66b422b..9af5e590 100644
--- a/src/plonk_challenger.rs
+++ b/src/plonk_challenger.rs
@@ -321,6 +321,7 @@ mod tests {
     use crate::field::crandall_field::CrandallField;
     use crate::field::field::Field;
     use crate::generator::generate_partial_witness;
+    use crate::permutation_argument::TargetPartitions;
     use crate::plonk_challenger::{Challenger, RecursiveChallenger};
     use crate::target::Target;
     use crate::witness::PartialWitness;
diff --git a/src/prover.rs b/src/prover.rs
index 5ea6ddfd..0d3f1be1 100644
--- a/src/prover.rs
+++ b/src/prover.rs
@@ -20,7 +20,7 @@ use crate::wire::Wire;
 use crate::witness::PartialWitness;
 
 pub(crate) fn prove<F: Extendable<D>, const D: usize>(
-    prover_data: &ProverOnlyCircuitData<F>,
+    prover_data: &ProverOnlyCircuitData<F, D>,
     common_data: &CommonCircuitData<F, D>,
     inputs: PartialWitness<F>,
 ) -> Proof<F, D> {
@@ -31,10 +31,17 @@ pub(crate) fn prove<F: Extendable<D>, const D: usize>(
     let mut witness = inputs;
     info!("Running {} generators", prover_data.generators.len());
     timed!(
-        generate_partial_witness(&mut witness, &prover_data.generators),
+        generate_partial_witness(&mut witness, &prover_data.generators,),
         "to generate witness"
     );
 
+    timed!(
+        witness
+            .check_copy_constraints(&prover_data.copy_constraints, &prover_data.gate_instances)
+            .unwrap(), // TODO: Change return value to `Result` and use `?` here.
+        "to check copy constraints"
+    );
+
     let config = &common_data.config;
     let num_wires = config.num_wires;
     let num_challenges = config.num_challenges;
@@ -159,7 +166,7 @@ fn compute_z<F: Extendable<D>, const D: usize>(
 
 fn compute_vanishing_polys<F: Extendable<D>, const D: usize>(
     common_data: &CommonCircuitData<F, D>,
-    prover_data: &ProverOnlyCircuitData<F>,
+    prover_data: &ProverOnlyCircuitData<F, D>,
     wires_commitment: &ListPolynomialCommitment<F>,
     plonk_zs_commitment: &ListPolynomialCommitment<F>,
     betas: &[F],
diff --git a/src/witness.rs b/src/witness.rs
index 5df8b238..989ec2bc 100644
--- a/src/witness.rs
+++ b/src/witness.rs
@@ -1,9 +1,12 @@
 use std::collections::HashMap;
 use std::convert::TryInto;
 
+use anyhow::{ensure, Result};
+
 use crate::field::extension_field::target::ExtensionTarget;
 use crate::field::extension_field::{Extendable, FieldExtension};
 use crate::field::field::Field;
+use crate::gates::gate::GateInstance;
 use crate::target::Target;
 use crate::wire::Wire;
 
@@ -121,6 +124,31 @@ impl<F: Field> PartialWitness<F> {
             self.set_target(target, value);
         }
     }
+
+    /// Checks that the copy constraints are satisfied in the witness.
+    pub fn check_copy_constraints<const D: usize>(
+        &self,
+        copy_constraints: &[(Target, Target)],
+        gate_instances: &[GateInstance<F, D>],
+    ) -> Result<()>
+    where
+        F: Extendable<D>,
+    {
+        for &(a, b) in copy_constraints {
+            // TODO: Take care of public inputs once they land.
+            if let (Target::Wire(wa), Target::Wire(wb)) = (a, b) {
+                let va = self.target_values.get(&a).copied().unwrap_or(F::ZERO);
+                let vb = self.target_values.get(&b).copied().unwrap_or(F::ZERO);
+                ensure!(
+                    va == vb,
+                    "Copy constraint between wire {} of gate #{} (`{}`) and wire {} of gate #{} (`{}`) is not satisfied. \
+                    Got values of {} and {} respectively.",
+                    wa.input, wa.gate, gate_instances[wa.gate].gate_type.0.id(), wb.input, wb.gate,
+                    gate_instances[wb.gate].gate_type.0.id(), va, vb);
+            }
+        }
+        Ok(())
+    }
 }
 
 impl<F: Field> Default for PartialWitness<F> {