diff --git a/lib/hcrypto/libtommath/bn_mp_mod.c b/lib/hcrypto/libtommath/bn_mp_mod.c
index 274e7dcd1..757335aeb 100644
--- a/lib/hcrypto/libtommath/bn_mp_mod.c
+++ b/lib/hcrypto/libtommath/bn_mp_mod.c
@@ -31,7 +31,7 @@ mp_mod (mp_int * a, mp_int * b, mp_int * c)
     return res;
   }
 
-  if (mp_iszero(&t) || t.sign == b.sign) {
+  if (mp_iszero(&t) || t.sign == b->sign) {
     res = MP_OKAY;
     mp_exch (&t, c);
   } else {