diff --git a/demo/timing.c b/demo/timing.c
index a7edb79..819cb5f 100644
--- a/demo/timing.c
+++ b/demo/timing.c
@@ -103,6 +103,10 @@ int main(void)
    uint64_t tt, gg, CLK_PER_SEC;
    FILE *log, *logb, *logc, *logd;
    mp_int a, b, c, d, e, f;
+#ifdef LTM_TIMING_PRIME_IS_PRIME
+   const char* name;
+   int m;
+#endif
    int n, cnt, ix, old_kara_m, old_kara_s, old_toom_m, old_toom_s;
    unsigned rr;
 
@@ -121,6 +125,40 @@ int main(void)
    CLK_PER_SEC = TIMFUNC() - CLK_PER_SEC;
 
    printf("CLK_PER_SEC == %" PRIu64 "\n", CLK_PER_SEC);
+
+#ifdef LTM_TIMING_PRIME_IS_PRIME
+   for (m = 0; m < 2; ++m) {
+      if (m == 0) {
+         name = "    Arnault";
+         mp_read_radix(&a,"91xLNF3roobhzgTzoFIG6P13ZqhOVYSN60Fa7Cj2jVR1g0k89zdahO9/kAiRprpfO1VAp1aBHucLFV/qLKLFb+zonV7R2Vxp1K13ClwUXStpV0oxTNQVjwybmFb5NBEHImZ6V7P6+udRJuH8VbMEnS0H8/pSqQrg82OoQQ2fPpAk6G1hkjqoCv5s/Yr",64);
+      } else {
+         name = "2^1119 + 53";
+         mp_set(&a,1u);
+         mp_mul_2d(&a,1119,&a);
+         mp_add_d(&a,53,&a);
+      }
+      cnt = mp_prime_rabin_miller_trials(mp_count_bits(&a));
+      ix = -cnt;
+      for (; cnt >= ix; cnt += ix) {
+         rr = 0u;
+         tt = UINT64_MAX;
+         do {
+            gg = TIMFUNC();
+            DO(mp_prime_is_prime(&a, cnt, &n));
+            gg = (TIMFUNC() - gg) >> 1;
+            if (tt > gg)
+               tt = gg;
+            if ((m == 0) && (n == MP_YES)) {
+               printf("Arnault's pseudoprime is not prime but mp_prime_is_prime says it is.\n");
+               return EXIT_FAILURE;
+            }
+         } while (++rr < 100u);
+         printf("Prime-check\t%s(%2d) => %9" PRIu64 "/sec, %9" PRIu64 " cycles\n",
+                name, cnt, CLK_PER_SEC / tt, tt);
+      }
+   }
+#endif
+
    log = FOPEN("logs/add.log", "w");
    for (cnt = 8; cnt <= 128; cnt += 8) {
       SLEEP;