diff --git a/bn_mp_cmp.c b/bn_mp_cmp.c
index 9047060..a505746 100644
--- a/bn_mp_cmp.c
+++ b/bn_mp_cmp.c
@@ -16,7 +16,7 @@
  */
 
 /* compare two ints (signed)*/
-int mp_cmp(mp_int *a, mp_int *b)
+int mp_cmp(const mp_int *a, mp_int *b)
 {
    /* compare based on sign */
    if (a->sign != b->sign) {
diff --git a/bn_mp_cmp_d.c b/bn_mp_cmp_d.c
index 27a546d..576a073 100644
--- a/bn_mp_cmp_d.c
+++ b/bn_mp_cmp_d.c
@@ -16,7 +16,7 @@
  */
 
 /* compare a digit */
-int mp_cmp_d(mp_int *a, mp_digit b)
+int mp_cmp_d(const mp_int *a, mp_digit b)
 {
    /* compare based on sign */
    if (a->sign == MP_NEG) {
diff --git a/bn_mp_cmp_mag.c b/bn_mp_cmp_mag.c
index ca2bc88..0066ca0 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(mp_int *a, mp_int *b)
+int mp_cmp_mag(const mp_int *a, mp_int *b)
 {
    int     n;
    mp_digit *tmpa, *tmpb;
diff --git a/bn_mp_cnt_lsb.c b/bn_mp_cnt_lsb.c
index 7273655..9a94d3d 100644
--- a/bn_mp_cnt_lsb.c
+++ b/bn_mp_cnt_lsb.c
@@ -20,7 +20,7 @@ static const int lnz[16] = {
 };
 
 /* Counts the number of lsbs which are zero before the first zero bit */
-int mp_cnt_lsb(mp_int *a)
+int mp_cnt_lsb(const mp_int *a)
 {
    int x;
    mp_digit q, qq;
diff --git a/bn_mp_copy.c b/bn_mp_copy.c
index bed03b2..17816e8 100644
--- a/bn_mp_copy.c
+++ b/bn_mp_copy.c
@@ -16,7 +16,7 @@
  */
 
 /* copy, b = a */
-int mp_copy(mp_int *a, mp_int *b)
+int mp_copy(const mp_int *a, mp_int *b)
 {
    int     res, n;
 
diff --git a/bn_mp_count_bits.c b/bn_mp_count_bits.c
index dea364f..7424581 100644
--- a/bn_mp_count_bits.c
+++ b/bn_mp_count_bits.c
@@ -16,7 +16,7 @@
  */
 
 /* returns the number of bits in an int */
-int mp_count_bits(mp_int *a)
+int mp_count_bits(const mp_int *a)
 {
    int     r;
    mp_digit q;
diff --git a/bn_mp_div_2d.c b/bn_mp_div_2d.c
index d6723ee..eae3498 100644
--- a/bn_mp_div_2d.c
+++ b/bn_mp_div_2d.c
@@ -16,7 +16,7 @@
  */
 
 /* shift right by a certain bit count (store quotient in c, optional remainder in d) */
-int mp_div_2d(mp_int *a, int b, mp_int *c, mp_int *d)
+int mp_div_2d(const mp_int *a, int b, mp_int *c, mp_int *d)
 {
    mp_digit D, r, rr;
    int     x, res;
diff --git a/bn_mp_init_copy.c b/bn_mp_init_copy.c
index c711e06..5681015 100644
--- a/bn_mp_init_copy.c
+++ b/bn_mp_init_copy.c
@@ -16,7 +16,7 @@
  */
 
 /* creates "a" then copies b into it */
-int mp_init_copy(mp_int *a, mp_int *b)
+int mp_init_copy(mp_int *a, const mp_int *b)
 {
    int     res;
 
diff --git a/bn_mp_mod_2d.c b/bn_mp_mod_2d.c
index 59270b9..8e69757 100644
--- a/bn_mp_mod_2d.c
+++ b/bn_mp_mod_2d.c
@@ -16,7 +16,7 @@
  */
 
 /* calc a value mod 2**b */
-int mp_mod_2d(mp_int *a, int b, mp_int *c)
+int mp_mod_2d(const mp_int *a, int b, mp_int *c)
 {
    int     x, res;
 
diff --git a/bn_mp_mul_2d.c b/bn_mp_mul_2d.c
index b3d92a9..4938e57 100644
--- a/bn_mp_mul_2d.c
+++ b/bn_mp_mul_2d.c
@@ -16,7 +16,7 @@
  */
 
 /* shift left by a certain bit count */
-int mp_mul_2d(mp_int *a, int b, mp_int *c)
+int mp_mul_2d(const mp_int *a, int b, mp_int *c)
 {
    mp_digit d;
    int      res;
diff --git a/bn_mp_neg.c b/bn_mp_neg.c
index b30d044..75f8bbd 100644
--- a/bn_mp_neg.c
+++ b/bn_mp_neg.c
@@ -16,7 +16,7 @@
  */
 
 /* b = -a */
-int mp_neg(mp_int *a, mp_int *b)
+int mp_neg(const mp_int *a, mp_int *b)
 {
    int     res;
    if (a != b) {
diff --git a/bn_mp_radix_size.c b/bn_mp_radix_size.c
index a6e2f04..29355cb 100644
--- a/bn_mp_radix_size.c
+++ b/bn_mp_radix_size.c
@@ -16,7 +16,7 @@
  */
 
 /* returns size of ASCII reprensentation */
-int mp_radix_size(mp_int *a, int radix, int *size)
+int mp_radix_size(const mp_int *a, int radix, int *size)
 {
    int     res, digs;
    mp_int  t;
diff --git a/tommath.h b/tommath.h
index 2aaea5b..3f49767 100644
--- a/tommath.h
+++ b/tommath.h
@@ -238,10 +238,10 @@ int mp_init_set(mp_int *a, mp_digit b);
 int mp_init_set_int(mp_int *a, unsigned long b);
 
 /* copy, b = a */
-int mp_copy(mp_int *a, mp_int *b);
+int mp_copy(const mp_int *a, mp_int *b);
 
 /* inits and copies, a = b */
-int mp_init_copy(mp_int *a, mp_int *b);
+int mp_init_copy(mp_int *a, const mp_int *b);
 
 /* trim unused digits */
 void mp_clamp(mp_int *a);
@@ -261,25 +261,25 @@ void mp_rshd(mp_int *a, int b);
 int mp_lshd(mp_int *a, int b);
 
 /* c = a / 2**b, implemented as c = a >> b */
-int mp_div_2d(mp_int *a, int b, mp_int *c, mp_int *d);
+int mp_div_2d(const mp_int *a, int b, mp_int *c, mp_int *d);
 
 /* b = a/2 */
 int mp_div_2(mp_int *a, mp_int *b);
 
 /* c = a * 2**b, implemented as c = a << b */
-int mp_mul_2d(mp_int *a, int b, mp_int *c);
+int mp_mul_2d(const mp_int *a, int b, mp_int *c);
 
 /* b = a*2 */
 int mp_mul_2(mp_int *a, mp_int *b);
 
 /* c = a mod 2**b */
-int mp_mod_2d(mp_int *a, int b, mp_int *c);
+int mp_mod_2d(const mp_int *a, int b, mp_int *c);
 
 /* computes a = 2**b */
 int mp_2expt(mp_int *a, int b);
 
 /* Counts the number of lsbs which are zero before the first zero bit */
-int mp_cnt_lsb(mp_int *a);
+int mp_cnt_lsb(const mp_int *a);
 
 /* I Love Earth! */
 
@@ -299,16 +299,16 @@ int mp_and(mp_int *a, mp_int *b, mp_int *c);
 /* ---> Basic arithmetic <--- */
 
 /* b = -a */
-int mp_neg(mp_int *a, mp_int *b);
+int mp_neg(const mp_int *a, mp_int *b);
 
 /* b = |a| */
 int mp_abs(mp_int *a, mp_int *b);
 
 /* compare a to b */
-int mp_cmp(mp_int *a, mp_int *b);
+int mp_cmp(const mp_int *a, const mp_int *b);
 
 /* compare |a| to |b| */
-int mp_cmp_mag(mp_int *a, mp_int *b);
+int mp_cmp_mag(const mp_int *a, const mp_int *b);
 
 /* c = a + b */
 int mp_add(mp_int *a, mp_int *b, mp_int *c);
@@ -331,7 +331,7 @@ int mp_mod(mp_int *a, mp_int *b, mp_int *c);
 /* ---> single digit functions <--- */
 
 /* compare against a single digit */
-int mp_cmp_d(mp_int *a, mp_digit b);
+int mp_cmp_d(const mp_int *a, mp_digit b);
 
 /* c = a + b */
 int mp_add_d(mp_int *a, mp_digit b, mp_int *c);
@@ -524,7 +524,7 @@ int mp_prime_next_prime(mp_int *a, int t, int bbs_style);
 int mp_prime_random_ex(mp_int *a, int t, int size, int flags, ltm_prime_callback cb, void *dat);
 
 /* ---> radix conversion <--- */
-int mp_count_bits(mp_int *a);
+int mp_count_bits(const mp_int *a);
 
 int mp_unsigned_bin_size(mp_int *a);
 int mp_read_unsigned_bin(mp_int *a, const unsigned char *b, int c);
@@ -539,7 +539,7 @@ int mp_to_signed_bin_n(mp_int *a, unsigned char *b, unsigned long *outlen);
 int mp_read_radix(mp_int *a, const char *str, int radix);
 int mp_toradix(mp_int *a, char *str, int radix);
 int mp_toradix_n(mp_int *a, char *str, int radix, int maxlen);
-int mp_radix_size(mp_int *a, int radix, int *size);
+int mp_radix_size(const mp_int *a, int radix, int *size);
 
 #ifndef LTM_NO_FILE
 int mp_fread(mp_int *a, int radix, FILE *stream);