diff --git a/amodem/common.py b/amodem/common.py
index 62791e2..d260016 100644
--- a/amodem/common.py
+++ b/amodem/common.py
@@ -41,7 +41,7 @@ def load(fileobj):
 
 
 def loads(data):
-    x = np.fromstring(str(data), dtype='int16')
+    x = np.frombuffer(data, dtype='int16')
     x = x / scaling
     return x
 
diff --git a/amodem/recv.py b/amodem/recv.py
index d6596df..2a7d116 100755
--- a/amodem/recv.py
+++ b/amodem/recv.py
@@ -287,8 +287,10 @@ if __name__ == '__main__':
     p = argparse.ArgumentParser()
     p.add_argument('--skip', type=int, default=100,
                    help='skip initial N samples, due to spurious spikes')
-    p.add_argument('-i', '--input', type=argparse.FileType('r'), default=sys.stdin)
-    p.add_argument('-o', '--output', type=argparse.FileType('w'), default=sys.stdout)
+    p.add_argument('-i', '--input', type=argparse.FileType('rb'),
+                   default=sys.stdin)
+    p.add_argument('-o', '--output', type=argparse.FileType('wb'),
+                   default=sys.stdout)
     args = p.parse_args()
     try:
         main(args)
diff --git a/amodem/send.py b/amodem/send.py
index 8f60210..fe9e7bf 100755
--- a/amodem/send.py
+++ b/amodem/send.py
@@ -34,7 +34,7 @@ class Writer(object):
 
     def write(self, fd, sym, n=1):
         data = common.dumps(sym, n)
-        fd.write(str(data))
+        fd.write(data)
         self.offset += len(data)
         if time.time() > self.last + 1:
             log.debug('%10.3f seconds of data audio',
@@ -99,9 +99,9 @@ if __name__ == '__main__':
     p = argparse.ArgumentParser()
     p.add_argument('--silence-start', type=float, default=1.0)
     p.add_argument('--silence-stop', type=float, default=1.0)
-    p.add_argument('-i', '--input', type=argparse.FileType('r'),
+    p.add_argument('-i', '--input', type=argparse.FileType('rb'),
                    default=sys.stdin)
-    p.add_argument('-o', '--output', type=argparse.FileType('w'),
+    p.add_argument('-o', '--output', type=argparse.FileType('wb'),
                    default=sys.stdout)
     args = p.parse_args()
     main(args)
diff --git a/tests/test_full.py b/tests/test_full.py
index 6fcd276..aa6c14d 100644
--- a/tests/test_full.py
+++ b/tests/test_full.py
@@ -18,18 +18,20 @@ class Args(object):
     def __init__(self, **kwargs):
         self.__dict__.update(kwargs)
 
+
 def run(size, chan):
     tx_data = os.urandom(size)
-    tx_audio = StringIO()
-    send.main(Args(silence_start=1, silence_stop=1, input=StringIO(tx_data), output=tx_audio))
+    tx_audio = BytesIO()
+    send.main(Args(silence_start=1, silence_stop=1,
+              input=BytesIO(tx_data), output=tx_audio))
 
     data = tx_audio.getvalue()
     data = common.loads(data)
     data = chan(data)
     data = common.dumps(data * 1j)
-    rx_audio = StringIO(data)
+    rx_audio = BytesIO(data)
 
-    rx_data = StringIO()
+    rx_data = BytesIO()
     recv.main(Args(skip=100, input=rx_audio, output=rx_data))
     rx_data = rx_data.getvalue()
 
diff --git a/tests/test_stream.py b/tests/test_stream.py
index e5b80bd..d4e3a07 100644
--- a/tests/test_stream.py
+++ b/tests/test_stream.py
@@ -1,14 +1,14 @@
 from amodem import stream
 import subprocess as sp
 
-script = r"""
+script = br"""
 import sys
 import time
 import os
 
 while True:
     time.sleep(0.1)
-    sys.stdout.write(b'\x00' * 6400)
+    sys.stdout.write('\x00' * 6400)
     sys.stderr.write('.')
 """