diff --git a/src/c_kzg.h b/src/c_kzg.h
index 70eec02..764703b 100644
--- a/src/c_kzg.h
+++ b/src/c_kzg.h
@@ -126,7 +126,7 @@ C_KZG_RET commit_to_poly(g1_t *out, const poly *p, const KZGSettings *ks);
 C_KZG_RET commit_to_poly_l(g1_t *out, const poly_l *p, const KZGSettings *ks);
 C_KZG_RET compute_proof_single(g1_t *out, const poly *p, const fr_t *x0, const KZGSettings *ks);
 C_KZG_RET compute_proof_single_l(g1_t *out, const poly_l *p, const fr_t *x0, const fr_t *y, const KZGSettings *ks);
-C_KZG_RET check_proof_single(bool *out, const g1_t *commitment, const g1_t *proof, const fr_t *x, fr_t *y,
+C_KZG_RET check_proof_single(bool *out, const g1_t *commitment, const g1_t *proof, const fr_t *x, const fr_t *y,
                              const KZGSettings *ks);
 C_KZG_RET compute_proof_multi(g1_t *out, const poly *p, const fr_t *x0, uint64_t n, const KZGSettings *ks);
 C_KZG_RET check_proof_multi(bool *out, const g1_t *commitment, const g1_t *proof, const fr_t *x, const fr_t *ys,
diff --git a/src/kzg_proofs.c b/src/kzg_proofs.c
index c442603..b120c88 100644
--- a/src/kzg_proofs.c
+++ b/src/kzg_proofs.c
@@ -103,7 +103,7 @@ C_KZG_RET compute_proof_single(g1_t *out, const poly *p, const fr_t *x0, const K
  * @param[in]  ks  The settings containing the secrets, previously initialised with #new_kzg_settings
  * @retval C_CZK_OK      All is well
  */
-C_KZG_RET check_proof_single(bool *out, const g1_t *commitment, const g1_t *proof, const fr_t *x, fr_t *y,
+C_KZG_RET check_proof_single(bool *out, const g1_t *commitment, const g1_t *proof, const fr_t *x, const fr_t *y,
                              const KZGSettings *ks) {
     g2_t x_g2, s_minus_x;
     g1_t y_g1, commitment_minus_y;