diff --git a/halo2_backend/src/plonk/vanishing/prover.rs b/halo2_backend/src/plonk/vanishing/prover.rs
index 96ce797ee..da56db956 100644
--- a/halo2_backend/src/plonk/vanishing/prover.rs
+++ b/halo2_backend/src/plonk/vanishing/prover.rs
@@ -117,7 +117,12 @@ impl<C: CurveAffine> Committed<C> {
         let h_poly = domain.divide_by_vanishing_poly(h_poly);
 
         // Obtain final h(X) polynomial
-        let h_poly = domain.extended_to_coeff(h_poly);
+        let mut h_poly = domain.extended_to_coeff(h_poly);
+
+        // Truncate it to match the size of the quotient polynomial; the
+        // evaluation domain might be slightly larger than necessary because
+        // it always lies on a power-of-two boundary.
+        h_poly.truncate(((1u64 << domain.k()) as usize) * domain.get_quotient_poly_degree());
 
         // Split h(X) up into pieces
         let h_pieces = h_poly
diff --git a/halo2_backend/src/poly/domain.rs b/halo2_backend/src/poly/domain.rs
index 5ca352e6c..706892677 100644
--- a/halo2_backend/src/poly/domain.rs
+++ b/halo2_backend/src/poly/domain.rs
@@ -328,7 +328,6 @@ impl<F: WithSmallOrderMulGroup<3>> EvaluationDomain<F> {
     ///
     /// This function will panic if the provided vector is not the correct
     /// length.
-    // TODO/FIXME: caller should be responsible for truncating
     pub fn extended_to_coeff(&self, mut a: Polynomial<F, ExtendedLagrangeCoeff>) -> Vec<F> {
         assert_eq!(a.values.len(), self.extended_len());
 
@@ -344,12 +343,6 @@ impl<F: WithSmallOrderMulGroup<3>> EvaluationDomain<F> {
         // transformation we performed earlier.
         self.distribute_powers_zeta(&mut a.values, false);
 
-        // Truncate it to match the size of the quotient polynomial; the
-        // evaluation domain might be slightly larger than necessary because
-        // it always lies on a power-of-two boundary.
-        a.values
-            .truncate((self.n * self.quotient_poly_degree) as usize);
-
         a.values
     }