diff --git a/library/bignum.c b/library/bignum.c
index 137afb07bc..bd09710ba4 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -2082,13 +2082,12 @@ cleanup:
 }
 
 /*
- * Modular inverse: X = A^-1 mod N  (HAC 14.61 / 14.64)
+ * Modular inverse: X = A^-1 mod N
+ *
+ * Wrapper around mbedtls_mpi_gcd_modinv_odd() that lifts its limitations.
  */
 int mbedtls_mpi_inv_mod(mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi *N)
 {
-    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    mbedtls_mpi G, TA, TU, U1, U2, TB, TV, V1, V2;
-
     if (mbedtls_mpi_cmp_int(N, 1) <= 0) {
         return MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
     }
@@ -2101,80 +2100,8 @@ int mbedtls_mpi_inv_mod(mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
         return mbedtls_mpi_inv_mod_even(X, A, N);
     }
 
-    mbedtls_mpi_init(&TA); mbedtls_mpi_init(&TU); mbedtls_mpi_init(&U1); mbedtls_mpi_init(&U2);
-    mbedtls_mpi_init(&G); mbedtls_mpi_init(&TB); mbedtls_mpi_init(&TV);
-    mbedtls_mpi_init(&V1); mbedtls_mpi_init(&V2);
-
-    MBEDTLS_MPI_CHK(mbedtls_mpi_gcd(&G, A, N));
-
-    if (mbedtls_mpi_cmp_int(&G, 1) != 0) {
-        ret = MBEDTLS_ERR_MPI_NOT_ACCEPTABLE;
-        goto cleanup;
-    }
-
-    MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(&TA, A, N));
-    MBEDTLS_MPI_CHK(mbedtls_mpi_copy(&TU, &TA));
-    MBEDTLS_MPI_CHK(mbedtls_mpi_copy(&TB, N));
-    MBEDTLS_MPI_CHK(mbedtls_mpi_copy(&TV, N));
-
-    MBEDTLS_MPI_CHK(mbedtls_mpi_lset(&U1, 1));
-    MBEDTLS_MPI_CHK(mbedtls_mpi_lset(&U2, 0));
-    MBEDTLS_MPI_CHK(mbedtls_mpi_lset(&V1, 0));
-    MBEDTLS_MPI_CHK(mbedtls_mpi_lset(&V2, 1));
-
-    do {
-        while ((TU.p[0] & 1) == 0) {
-            MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(&TU, 1));
-
-            if ((U1.p[0] & 1) != 0 || (U2.p[0] & 1) != 0) {
-                MBEDTLS_MPI_CHK(mbedtls_mpi_add_mpi(&U1, &U1, &TB));
-                MBEDTLS_MPI_CHK(mbedtls_mpi_sub_mpi(&U2, &U2, &TA));
-            }
-
-            MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(&U1, 1));
-            MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(&U2, 1));
-        }
-
-        while ((TV.p[0] & 1) == 0) {
-            MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(&TV, 1));
-
-            if ((V1.p[0] & 1) != 0 || (V2.p[0] & 1) != 0) {
-                MBEDTLS_MPI_CHK(mbedtls_mpi_add_mpi(&V1, &V1, &TB));
-                MBEDTLS_MPI_CHK(mbedtls_mpi_sub_mpi(&V2, &V2, &TA));
-            }
-
-            MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(&V1, 1));
-            MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(&V2, 1));
-        }
-
-        if (mbedtls_mpi_cmp_mpi(&TU, &TV) >= 0) {
-            MBEDTLS_MPI_CHK(mbedtls_mpi_sub_mpi(&TU, &TU, &TV));
-            MBEDTLS_MPI_CHK(mbedtls_mpi_sub_mpi(&U1, &U1, &V1));
-            MBEDTLS_MPI_CHK(mbedtls_mpi_sub_mpi(&U2, &U2, &V2));
-        } else {
-            MBEDTLS_MPI_CHK(mbedtls_mpi_sub_mpi(&TV, &TV, &TU));
-            MBEDTLS_MPI_CHK(mbedtls_mpi_sub_mpi(&V1, &V1, &U1));
-            MBEDTLS_MPI_CHK(mbedtls_mpi_sub_mpi(&V2, &V2, &U2));
-        }
-    } while (mbedtls_mpi_cmp_int(&TU, 0) != 0);
-
-    while (mbedtls_mpi_cmp_int(&V1, 0) < 0) {
-        MBEDTLS_MPI_CHK(mbedtls_mpi_add_mpi(&V1, &V1, N));
-    }
-
-    while (mbedtls_mpi_cmp_mpi(&V1, N) >= 0) {
-        MBEDTLS_MPI_CHK(mbedtls_mpi_sub_mpi(&V1, &V1, N));
-    }
-
-    MBEDTLS_MPI_CHK(mbedtls_mpi_copy(X, &V1));
-
-cleanup:
-
-    mbedtls_mpi_free(&TA); mbedtls_mpi_free(&TU); mbedtls_mpi_free(&U1); mbedtls_mpi_free(&U2);
-    mbedtls_mpi_free(&G); mbedtls_mpi_free(&TB); mbedtls_mpi_free(&TV);
-    mbedtls_mpi_free(&V1); mbedtls_mpi_free(&V2);
-
-    return ret;
+    /* If A and N are both even, 2 divides they GCD, so no inverse. */
+    return MBEDTLS_ERR_MPI_NOT_ACCEPTABLE;
 }
 
 #if defined(MBEDTLS_GENPRIME)