c3-lang/libtommath

diff --git a/bn_mp_rand.c b/bn_mp_rand.c
index 83afe27..2ed665e 100644
--- a/bn_mp_rand.c
+++ b/bn_mp_rand.c
@@ -15,6 +15,9 @@
  * Tom St Denis, tstdenis82@gmail.com, http://libtom.org
  */
 
+#if defined(MP_8BIT) || defined(MP_16BIT)
+#define MP_GEN_RANDOM_SHIFT  DIGIT_BIT
+#else
 #if MP_GEN_RANDOM_MAX == 0xffffffffu
 #define MP_GEN_RANDOM_SHIFT  32
 #elif MP_GEN_RANDOM_MAX == 32767
@@ -26,6 +29,7 @@
 #elif !defined(MP_GEN_RANDOM_SHIFT)
 #error Thou shalt define their own valid MP_GEN_RANDOM_SHIFT
 #endif
+#endif
 
 /* makes a pseudo-random int of a given size */
 static mp_digit s_gen_random(void)