diff --git a/graphenebase/types.py b/graphenebase/types.py
index ce8efa25..1549db9c 100644
--- a/graphenebase/types.py
+++ b/graphenebase/types.py
@@ -211,7 +211,7 @@ def __init__(self, d):
         self.data = d
 
     def __bytes__(self):
-        return struct.pack("<I", timegm(time.strptime((self.data + "UTC"), timeformat)))
+        return struct.pack("<i", timegm(time.strptime((self.data + "UTC"), timeformat)))
 
     def __str__(self):
         return self.data
diff --git a/setup.py b/setup.py
index eb336059..bae36a5c 100755
--- a/setup.py
+++ b/setup.py
@@ -11,7 +11,7 @@
     ascii = codecs.lookup('ascii')
     codecs.register(lambda name, enc=ascii: {True: enc}.get(name == 'mbcs'))
 
-VERSION = '0.5.7'
+VERSION = '0.5.8'
 
 setup(
     name='graphenelib',
diff --git a/tox.ini b/tox.ini
index 26111811..39fbfbf7 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,6 @@
 [tox]
 envlist = py35,py36,py37,lint,docs
+skip_missing_interpreters = true
 
 [testenv]
 deps = -rrequirements-test.txt