diff --git a/.gitignore b/.gitignore
index 71b79d3..b11bdd6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,8 +1,9 @@
+*.egg-info
 *.pyc
-.coverage
-.venv
-build
-dist
-extras
-iptools.egg-info
+/.coverage
+/.tox/
+/.venv/
+/build/
+/dist/
+/extras/
 setuptools-*.egg
diff --git a/.travis.yml b/.travis.yml
index eada3f2..70c1d3c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,16 +1,22 @@
 language: python
 python:
-  - "2.6"
   - "2.7"
-  - "3.2"
-  - "3.3"
+  - "3.4"
+  - "3.5"
   - "pypy"
+  - "pypy3"
+sudo: false
+matrix:
+  fast_finish: true
+
 install:
-  - pip install .
-  - pip install -r tests/requirements.txt
+  - pip install wheel tox-travis
+  - python setup.py install bdist_wheel
+  - pip install ./dist/iptools-*.whl
 script:
-  - flake8
-  - nosetests
+  - tox
+  - tox --installpkg ./dist/iptools-*.whl
+
 notifications:
   email:
       - travis-ci+python-iptools@bd808.com
diff --git a/iptools/__init__.py b/iptools/__init__.py
index 608ea4b..181f845 100644
--- a/iptools/__init__.py
+++ b/iptools/__init__.py
@@ -22,13 +22,6 @@
 # CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 # ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
-__version__ = '0.7.0-dev'
-
-__all__ = (
-    'IpRange',
-    'IpRangeList',
-)
-
 
 # sniff for python2.x / python3k compatibility "fixes'
 try:
@@ -51,10 +44,16 @@ def next(iterable):
     Sequence = object
 # end compatibility "fixes'
 
-
 from . import ipv4
 from . import ipv6
 
+__version__ = '0.7.0-dev'
+
+__all__ = (
+    'IpRange',
+    'IpRangeList',
+)
+
 
 def _address2long(address):
     """
diff --git a/iptools/ipv4.py b/iptools/ipv4.py
index c3d0127..3243482 100644
--- a/iptools/ipv4.py
+++ b/iptools/ipv4.py
@@ -23,6 +23,40 @@
 # ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
 
+import re
+
+# sniff for python2.x / python3k compatibility "fixes'
+try:
+    basestring = basestring
+except NameError:
+    # 'basestring' is undefined, must be python3k
+    basestring = str
+
+try:
+    bin = bin
+except NameError:
+    # builtin bin function doesn't exist
+    def bin(x):
+        """
+        From http://code.activestate.com/recipes/219300/#c7
+        """
+        if x < 0:
+            return '-' + bin(-x)
+        out = []
+        if x == 0:
+            out.append('0')
+        while x > 0:
+            out.append('01'[x & 1])
+            x >>= 1
+            pass
+        try:
+            return '0b' + ''.join(reversed(out))
+        except NameError:
+            out.reverse()
+            return '0b' + ''.join(out)
+    # end bin
+# end compatibility "fixes'
+
 __all__ = (
     'cidr2block',
     'hex2ip',
@@ -60,43 +94,6 @@
     'TEST_NET_3',
 )
 
-
-import re
-
-
-# sniff for python2.x / python3k compatibility "fixes'
-try:
-    basestring = basestring
-except NameError:
-    # 'basestring' is undefined, must be python3k
-    basestring = str
-
-try:
-    bin = bin
-except NameError:
-    # builtin bin function doesn't exist
-    def bin(x):
-        """
-        From http://code.activestate.com/recipes/219300/#c7
-        """
-        if x < 0:
-            return '-' + bin(-x)
-        out = []
-        if x == 0:
-            out.append('0')
-        while x > 0:
-            out.append('01'[x & 1])
-            x >>= 1
-            pass
-        try:
-            return '0b' + ''.join(reversed(out))
-        except NameError:
-            out.reverse()
-            return '0b' + ''.join(out)
-    # end bin
-# end compatibility "fixes'
-
-
 #: Regex for validating an IPv4 address
 _DOTTED_QUAD_RE = re.compile(r'^(\d{1,3}\.){0,3}\d{1,3}$')
 
@@ -285,6 +282,10 @@ def validate_netmask(s):
     True
     >>> validate_netmask('128.0.0.1')
     False
+    >>> validate_netmask('1.255.255.0')
+    False
+    >>> validate_netmask('0.255.255.0')
+    False
 
 
     :param s: String to validate as a dotted-quad notation netmask.
@@ -293,7 +294,8 @@ def validate_netmask(s):
     :raises: TypeError
     """
     if validate_ip(s):
-        mask = bin(ip2network(s))[2:]
+        # Convert to binary string, strip '0b' prefix, 0 pad to 32 bits
+        mask = bin(ip2network(s))[2:].zfill(32)
         # all left most bits must be 1, all right most must be 0
         seen0 = False
         for c in mask:
diff --git a/iptools/ipv6.py b/iptools/ipv6.py
index 9fab832..97d00ee 100644
--- a/iptools/ipv6.py
+++ b/iptools/ipv6.py
@@ -23,6 +23,9 @@
 # ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
 
+import re
+from . import ipv4
+
 __all__ = (
     'cidr2block',
     'ip2long',
@@ -52,11 +55,6 @@
     'UNSPECIFIED_ADDRESS',
 )
 
-
-import re
-from . import ipv4
-
-
 #: Regex for validating an IPv6 in hex notation
 _HEX_RE = re.compile(r'^([0-9a-f]{0,4}:){2,7}[0-9a-f]{0,4}$')
 
diff --git a/setup.cfg b/setup.cfg
index ec2d4e2..85d3e9c 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,18 +1,19 @@
 [nosetests]
+verbosity=2
 detailed-errors=1
 with-coverage=1
 with-doctest=1
 cover-package=iptools
 cover-html=1
 cover-html-dir=docs/_build/cover
+cover-branches=1
 
 [flake8]
-ignore=F821,E402
 count=1
 show-pep8=1
 show-source=1
 statistics=1
-exclude=build,dist,docs,*.egg,*.egg-info
+exclude=.tox,.venv,build,dist,docs,*.egg,*.egg-info
 
 [wheel]
 universal = 1
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 0000000..a99d698
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,8 @@
+[tox]
+envlist = py27, py34, py35, pypy, pypy3
+
+[testenv]
+deps = -r{toxinidir}/tests/requirements.txt
+commands =
+    flake8
+    nosetests