diff --git a/src/kzg_single_proofs.c b/src/kzg_single_proofs.c
index 7766fc2..fc9911c 100644
--- a/src/kzg_single_proofs.c
+++ b/src/kzg_single_proofs.c
@@ -21,9 +21,12 @@ void commit_to_poly(blst_p1 *out, const KZGSettings *ks, const poly *p) {
 }
 
 // Compute KZG proof for polynomial at position x0
-void compute_proof_single(blst_p1 *out, const KZGSettings *ks, poly *p, const uint64_t x0) {
+C_KZG_RET compute_proof_single(blst_p1 *out, const KZGSettings *ks, poly *p, const uint64_t x0) {
     poly divisor, q;
     blst_fr tmp;
+    uint64_t len;
+
+    ASSERT(p->length >= 2, C_KZG_BADARGS);
 
     // The divisor is x - x0
     poly_init(&divisor, 2);
@@ -32,13 +35,17 @@ void compute_proof_single(blst_p1 *out, const KZGSettings *ks, poly *p, const ui
     divisor.coeffs[1] = one;
 
     // Calculate q = p / (x - x0)
-    poly_init(&q, poly_quotient_length(p, &divisor));
-    poly_long_div(&q, p, &divisor);
+    // Discard the return codes since we already checked above that all should be fine.
+    (void) poly_quotient_length(&len, p, &divisor);
+    poly_init(&q, len);
+    (void) poly_long_div(&q, p, &divisor);
 
     linear_combination_g1(out, ks->secret_g1, q.coeffs, q.length);
 
     poly_free(q);
     poly_free(divisor);
+
+    return C_KZG_OK;
 }
 
 bool check_proof_single(const KZGSettings *ks, const blst_p1 *commitment, const blst_p1 *proof, const blst_fr *x, blst_fr *y) {
diff --git a/src/kzg_single_proofs.h b/src/kzg_single_proofs.h
index 84fa203..d66cfa8 100644
--- a/src/kzg_single_proofs.h
+++ b/src/kzg_single_proofs.h
@@ -19,5 +19,5 @@
 #include "poly.h"
 
 void commit_to_poly(blst_p1 *out, const KZGSettings *ks, const poly *p);
-void compute_proof_single(blst_p1 *out, const KZGSettings *ks, poly *p, const uint64_t x0);
+C_KZG_RET compute_proof_single(blst_p1 *out, const KZGSettings *ks, poly *p, const uint64_t x0);
 bool check_proof_single(const KZGSettings *ks, const blst_p1 *commitment, const blst_p1 *proof, const blst_fr *x, blst_fr *y);
diff --git a/src/kzg_single_proofs_test.c b/src/kzg_single_proofs_test.c
index 873426c..d28f745 100644
--- a/src/kzg_single_proofs_test.c
+++ b/src/kzg_single_proofs_test.c
@@ -58,7 +58,7 @@ void proof_single(void) {
     new_kzg_settings(&ks, &fs, s1, s2, 17);
 
     commit_to_poly(&commitment, &ks, &p);
-    compute_proof_single(&proof, &ks, &p, 17);
+    TEST_CHECK(C_KZG_OK == compute_proof_single(&proof, &ks, &p, 17));
 
     fr_from_uint64(&x, 17);
     poly_eval(&value, &p, &x);
@@ -69,9 +69,23 @@ void proof_single(void) {
     free(s2);
 }
 
+void proof_single_error(void) {
+    poly p;
+    blst_p1 proof;
+    KZGSettings ks;
+
+    // Check it barfs on a constant polynomial
+    poly_init(&p, 1);
+
+    TEST_CHECK(C_KZG_BADARGS == compute_proof_single(&proof, &ks, &p, 17));
+
+    poly_free(p);
+}
+
 TEST_LIST =
     {
      {"KZG_SINGLE_PRROFS_TEST", title},
      {"proof_single", proof_single},
+     {"proof_single_error", proof_single},
      { NULL, NULL }     /* zero record marks the end of the list */
     };
diff --git a/src/poly.c b/src/poly.c
index 329b6e2..bbd64f2 100644
--- a/src/poly.c
+++ b/src/poly.c
@@ -47,8 +47,10 @@ void poly_eval(blst_fr *out, const poly *p, const blst_fr *x) {
 }
 
 // Call this to find out how much space to allocate for the result
-uint64_t poly_quotient_length(const poly *dividend, const poly *divisor) {
-    return dividend->length - divisor->length + 1;
+C_KZG_RET poly_quotient_length(uint64_t *out, const poly *dividend, const poly *divisor) {
+    ASSERT(dividend->length >= divisor->length, C_KZG_BADARGS);
+    *out = dividend->length - divisor->length + 1;
+    return C_KZG_OK;
 }
 
 // `out` must have been pre-allocated to the correct size, and the length is provided
diff --git a/src/poly.h b/src/poly.h
index 123d590..8c92a07 100644
--- a/src/poly.h
+++ b/src/poly.h
@@ -26,5 +26,5 @@ typedef struct {
 void poly_init(poly *out, const uint64_t length);
 void poly_free(poly p);
 void poly_eval(blst_fr *out, const poly *p, const blst_fr *x);
-uint64_t poly_quotient_length(const poly *dividend, const poly *divisor);
+C_KZG_RET poly_quotient_length(uint64_t *out, const poly *dividend, const poly *divisor);
 C_KZG_RET poly_long_div(poly *out, const poly *dividend, const poly *divisor);
diff --git a/src/poly_test.c b/src/poly_test.c
index c54f0a8..cf40779 100644
--- a/src/poly_test.c
+++ b/src/poly_test.c
@@ -22,9 +22,19 @@ void title(void) {;}
 
 void poly_div_length(void) {
     poly a, b;
+    uint64_t len;
     poly_init(&a, 17);
     poly_init(&b, 5);
-    TEST_CHECK(13 == poly_quotient_length(&a, &b));
+    TEST_CHECK(C_KZG_OK == poly_quotient_length(&len, &a, &b));
+    TEST_CHECK(13 == len);
+}
+
+void poly_div_length_bad(void) {
+    poly a, b;
+    uint64_t len;
+    poly_init(&a, 5);
+    poly_init(&b, 17);
+    TEST_CHECK(C_KZG_BADARGS == poly_quotient_length(&len, &a, &b));
 }
 
 void poly_div_0(void) {
@@ -55,7 +65,7 @@ void poly_div_0(void) {
     actual.length = 2;
     actual.coeffs = c;
 
-    TEST_CHECK(poly_long_div(&actual, &dividend, &divisor) == C_KZG_OK);
+    TEST_CHECK(C_KZG_OK == poly_long_div(&actual, &dividend, &divisor));
     TEST_CHECK(fr_equal(&expected[0], &actual.coeffs[0]));
     TEST_CHECK(fr_equal(&expected[1], &actual.coeffs[1]));
 }
@@ -90,7 +100,7 @@ void poly_div_1(void) {
     actual.length = 3;
     actual.coeffs = c;
 
-    TEST_CHECK(poly_long_div(&actual, &dividend, &divisor) == C_KZG_OK);
+    TEST_CHECK(C_KZG_OK == poly_long_div(&actual, &dividend, &divisor));
     TEST_CHECK(fr_equal(&expected[0], &actual.coeffs[0]));
     TEST_CHECK(fr_equal(&expected[1], &actual.coeffs[1]));
     TEST_CHECK(fr_equal(&expected[2], &actual.coeffs[2]));
@@ -98,7 +108,7 @@ void poly_div_1(void) {
 
 void poly_wrong_size(void) {
     poly dividend, divisor, result;
-    TEST_CHECK(poly_long_div(&result, &dividend, &divisor) == C_KZG_BADARGS);
+    TEST_CHECK(C_KZG_BADARGS == poly_long_div(&result, &dividend, &divisor));
 }
 
 void poly_eval_check(void) {
@@ -120,6 +130,7 @@ TEST_LIST =
     {
      {"POLY_TEST", title},
      {"poly_div_length", poly_div_length},
+     {"poly_div_length_bad", poly_div_length_bad},
      {"poly_div_0", poly_div_0},
      {"poly_div_1", poly_div_1},
      {"poly_wrong_size", poly_wrong_size},