diff --git a/src/testrand.h b/src/testrand.h
index ac9950c..041bb92 100644
--- a/src/testrand.h
+++ b/src/testrand.h
@@ -14,7 +14,7 @@
 /* A non-cryptographic RNG used only for test infrastructure. */
 
 /** Seed the pseudorandom number generator for testing. */
-SECP256K1_INLINE static void secp256k1_rand_seed(uint64_t v);
+SECP256K1_INLINE static void secp256k1_rand_seed(const unsigned char *seed16);
 
 /** Generate a pseudorandom 32-bit number. */
 static uint32_t secp256k1_rand32(void);
diff --git a/src/testrand_impl.h b/src/testrand_impl.h
index 42b23e8..36b0534 100644
--- a/src/testrand_impl.h
+++ b/src/testrand_impl.h
@@ -17,8 +17,8 @@ static secp256k1_rfc6979_hmac_sha256_t secp256k1_test_rng;
 static uint32_t secp256k1_test_rng_precomputed[8];
 static int secp256k1_test_rng_precomputed_used = 8;
 
-SECP256K1_INLINE static void secp256k1_rand_seed(uint64_t v) {
-    secp256k1_rfc6979_hmac_sha256_initialize(&secp256k1_test_rng, (const unsigned char*)"PRNG", 4, (const unsigned char*)&v, sizeof(v));
+SECP256K1_INLINE static void secp256k1_rand_seed(const unsigned char *seed16) {
+    secp256k1_rfc6979_hmac_sha256_initialize(&secp256k1_test_rng, (const unsigned char*)"TestRNG", 7, seed16, 16);
 }
 
 SECP256K1_INLINE static uint32_t secp256k1_rand32(void) {
diff --git a/src/tests.c b/src/tests.c
index 313c0cc..b8471d0 100644
--- a/src/tests.c
+++ b/src/tests.c
@@ -1763,7 +1763,8 @@ void run_ecdsa_openssl(void) {
 #endif
 
 int main(int argc, char **argv) {
-    uint64_t seed;
+    unsigned char seed16[16] = {0};
+    unsigned char run32[32] = {0};
     /* find iteration count */
     if (argc > 1) {
         count = strtol(argv[1], NULL, 0);
@@ -1771,18 +1772,37 @@ int main(int argc, char **argv) {
 
     /* find random seed */
     if (argc > 2) {
-        sscanf(argv[2], "%" I64uFORMAT, (unsigned long long*)&seed);
+        int pos = 0;
+        const char* ch = argv[2];
+        while (pos < 16 && ch[0] != 0 && ch[1] != 0) {
+            unsigned short sh;
+            if (sscanf(ch, "%2hx", &sh)) {
+                seed16[pos] = sh;
+            } else {
+                break;
+            }
+            ch += 2;
+            pos++;
+        }
     } else {
         FILE *frand = fopen("/dev/urandom", "r");
-        if (!frand || !fread(&seed, sizeof(seed), 1, frand)) {
-            seed = time(NULL) * 1337;
+        if (!frand || !fread(&seed16, sizeof(seed16), 1, frand)) {
+            uint64_t t = time(NULL) * (uint64_t)1337;
+            seed16[0] ^= t;
+            seed16[1] ^= t >> 8;
+            seed16[2] ^= t >> 16;
+            seed16[3] ^= t >> 24;
+            seed16[4] ^= t >> 32;
+            seed16[5] ^= t >> 40;
+            seed16[6] ^= t >> 48;
+            seed16[7] ^= t >> 56;
         }
         fclose(frand);
     }
-    secp256k1_rand_seed(seed);
+    secp256k1_rand_seed(seed16);
 
     printf("test count = %i\n", count);
-    printf("random seed = %" I64uFORMAT "\n", (unsigned long long)seed);
+    printf("random seed = %02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x\n", seed16[0], seed16[1], seed16[2], seed16[3], seed16[4], seed16[5], seed16[6], seed16[7], seed16[8], seed16[9], seed16[10], seed16[11], seed16[12], seed16[13], seed16[14], seed16[15]);
 
     /* initialize */
     secp256k1_start(SECP256K1_START_SIGN | SECP256K1_START_VERIFY);
@@ -1828,7 +1848,8 @@ int main(int argc, char **argv) {
     run_ecdsa_openssl();
 #endif
 
-    printf("random run = %llu\n", (unsigned long long)secp256k1_rand32() + ((unsigned long long)secp256k1_rand32() << 32));
+    secp256k1_rand256(run32);
+    printf("random run = %02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x\n", run32[0], run32[1], run32[2], run32[3], run32[4], run32[5], run32[6], run32[7], run32[8], run32[9], run32[10], run32[11], run32[12], run32[13], run32[14], run32[15]);
 
     /* shutdown */
     secp256k1_stop();