diff --git a/escpos/escpos.py b/escpos/escpos.py
index 4498456..738c258 100644
--- a/escpos/escpos.py
+++ b/escpos/escpos.py
@@ -83,7 +83,7 @@ class Escpos(object):
         pbuffer = b''
 
         self._raw(S_RASTER_N)
-        pbuffer = "%02X%02X%02X%02X" % (((size[0]/size[1])/8), 0, size[1] & 0xff, size[1] >> 8)
+        pbuffer = "%02X%02X%02X%02X" % (((size[0]//size[1])//8), 0, size[1] & 0xff, size[1] >> 8)
         self._raw(binascii.unhexlify(pbuffer))
         pbuffer = ""
 
diff --git a/tox.ini b/tox.ini
index 0a56f96..c7460c5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py27, py34
+envlist = py27, py34, py35
 
 [testenv]
 deps = nose