diff --git a/test/cryptsuite.py b/test/cryptsuite.py
index 02f77d56..e6f638d6 100755
--- a/test/cryptsuite.py
+++ b/test/cryptsuite.py
@@ -103,6 +103,12 @@ def queued_specific_random_data(data):
     yield None
     random_clear()
 
+@contextlib.contextmanager
+def random_prng(seed):
+    random_make_prng('sha256', seed)
+    yield None
+    random_clear()
+
 def hash_str(alg, message):
     h = ssh_hash_new(alg)
     ssh_hash_update(h, message)
diff --git a/testcrypt.c b/testcrypt.c
index 94d9baaf..e01ed606 100644
--- a/testcrypt.c
+++ b/testcrypt.c
@@ -55,10 +55,15 @@ static bool old_keyfile_warning_given;
 void old_keyfile_warning(void) { old_keyfile_warning_given = true; }
 
 static bufchain random_data_queue;
+static prng *test_prng;
 void random_read(void *buf, size_t size)
 {
-    if (!bufchain_try_fetch_consume(&random_data_queue, buf, size))
-        fatal_error("No random data in queue");
+    if (test_prng) {
+        prng_read(test_prng, buf, size);
+    } else {
+        if (!bufchain_try_fetch_consume(&random_data_queue, buf, size))
+            fatal_error("No random data in queue");
+    }
 }
 
 uint64_t prng_reseed_time_ms(void)
@@ -673,9 +678,24 @@ static size_t random_queue_len(void)
 
 static void random_clear(void)
 {
+    if (test_prng) {
+        prng_free(test_prng);
+        test_prng = NULL;
+    }
+
     bufchain_clear(&random_data_queue);
 }
 
+static void random_make_prng(const ssh_hashalg *hashalg, ptrlen seed)
+{
+    random_clear();
+
+    test_prng = prng_new(hashalg);
+    prng_seed_begin(test_prng);
+    put_datapl(test_prng, seed);
+    prng_seed_finish(test_prng);
+}
+
 mp_int *monty_identity_wrapper(MontyContext *mc)
 {
     return mp_copy(monty_identity(mc));
diff --git a/testcrypt.h b/testcrypt.h
index 2fec0ba2..4ed190af 100644
--- a/testcrypt.h
+++ b/testcrypt.h
@@ -290,4 +290,5 @@ FUNC2(boolean, crcda_detect, val_string_ptrlen, val_string_ptrlen)
  */
 FUNC1(void, random_queue, val_string_ptrlen)
 FUNC0(uint, random_queue_len)
+FUNC2(void, random_make_prng, hashalg, val_string_ptrlen)
 FUNC0(void, random_clear)