diff --git a/src/highlevelcrypto.py b/src/highlevelcrypto.py
index 551aa376..e0b86f35 100644
--- a/src/highlevelcrypto.py
+++ b/src/highlevelcrypto.py
@@ -85,7 +85,12 @@ def random_keys():
 
 def deterministic_keys(passphrase, nonce):
     """Generate keys from *passphrase* and *nonce* (encoded as varint)"""
-    priv = hashlib.sha512(passphrase.encode() + nonce).digest()[:32]
+    if isinstance(passphrase, str):
+        ph = passphrase.encode()
+    else:
+        ph = passphrase
+    priv = hashlib.sha512(ph + nonce).digest()[:32]
+
     pub = pointMult(priv)
     return priv, pub
 
diff --git a/src/tests/test_randomtrackingdict.py b/src/tests/test_randomtrackingdict.py
index 2db3c423..cbe0ee55 100644
--- a/src/tests/test_randomtrackingdict.py
+++ b/src/tests/test_randomtrackingdict.py
@@ -15,10 +15,10 @@ class TestRandomTrackingDict(unittest.TestCase):
     @staticmethod
     def randString():
         """helper function for tests, generates a random string"""
-        retval = ''
-        for _ in range(32):
-            retval += chr(random.randint(0, 255))
-        return retval
+        retval = bytearray(32)
+        for i in range(32):
+            retval[i] = random.randint(0, 255)
+        return bytes(retval)
 
     def test_check_randomtrackingdict(self):
         """Check the logic of RandomTrackingDict class"""