diff --git a/bn_mp_cmp.c b/bn_mp_cmp.c
index a505746..a33d483 100644
--- a/bn_mp_cmp.c
+++ b/bn_mp_cmp.c
@@ -16,7 +16,7 @@
  */
 
 /* compare two ints (signed)*/
-int mp_cmp(const mp_int *a, mp_int *b)
+int mp_cmp(const mp_int *a, const mp_int *b)
 {
    /* compare based on sign */
    if (a->sign != b->sign) {
diff --git a/bn_mp_cmp_mag.c b/bn_mp_cmp_mag.c
index 0066ca0..e2c723f 100644
--- a/bn_mp_cmp_mag.c
+++ b/bn_mp_cmp_mag.c
@@ -16,7 +16,7 @@
  */
 
 /* compare maginitude of two ints (unsigned) */
-int mp_cmp_mag(const mp_int *a, mp_int *b)
+int mp_cmp_mag(const mp_int *a, const mp_int *b)
 {
    int     n;
    mp_digit *tmpa, *tmpb;