diff --git a/disco/voice/opus.py b/disco/voice/opus.py
index 246dbed..b33cff8 100644
--- a/disco/voice/opus.py
+++ b/disco/voice/opus.py
@@ -1,3 +1,4 @@
+import six
 import sys
 import array
 import ctypes
@@ -142,7 +143,10 @@ class OpusEncoder(BaseOpus):
             raise Exception('Failed to encode: {}'.format(ret))
 
         # TODO: py3
-        return array.array('b', data[:ret]).tostring()
+        if six.PY3:
+            return array.array('b', data[:ret]).tobytes()
+        else:
+            return array.array('b', data[:ret]).tostring()
 
 
 class OpusDecoder(BaseOpus):
diff --git a/requirements.txt b/requirements.txt
index a0de4f3..066c0b1 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,5 @@
 gevent==1.2.1
-holster==1.0.14
+holster==1.0.15
 inflection==0.3.1
 requests==2.13.0
 six==1.10.0