diff --git a/pip_install_privates/install.py b/pip_install_privates/install.py
index db7eee3..acc62b1 100644
--- a/pip_install_privates/install.py
+++ b/pip_install_privates/install.py
@@ -100,7 +100,8 @@ are also stripped of the -e flag. If no token is given, private URLs will be
 kept, including the -e flag (otherwise they can't be installed at all).
 """)
 
-    parser.add_argument('--token', '-t', help='Your Personal Access Token for private GitHub repositories')
+    parser.add_argument('--token', '-t', help='Your Personal Access Token for private GitHub repositories',
+                        default=os.environ.get('GITHUB_TOKEN'))
     parser.add_argument('req_file', help='path to the requirements file to install')
     args = parser.parse_args()
 
diff --git a/setup.py b/setup.py
index 950654e..2df3987 100644
--- a/setup.py
+++ b/setup.py
@@ -11,7 +11,7 @@ def readfile(filename):
 
 setup(
     name='pip_install_privates',
-    version='0.5.1',
+    version='0.5.2',
     description='Install pip packages from private repositories without an ssh agent',
     long_description=readfile('README.rst'),
     long_description_content_type='text/x-rst',

diff --git a/tests/unit/test_commandline.py b/tests/unit/test_commandline.py
index b694c25..eba89c5 100644
--- a/tests/unit/test_commandline.py
+++ b/tests/unit/test_commandline.py
@@ -40,6 +40,21 @@ class TestCommandLine(TestCase):
         self.mock_collect.assert_called_once_with('requirements.txt',
                                                   transform_with_token='my-token')
 
+    def test_uses_github_token_environment_variable_if_no_token_supplied(self):
+        with patch.dict('pip_install_privates.install.os.environ', {'GITHUB_TOKEN': 'my-token'}):
+            with patch.object(sys, 'argv', ['pip-install', 'requirements.txt']):
+                install()
+
+        self.mock_collect.assert_called_once_with('requirements.txt',
+                                                  transform_with_token='my-token')
+
+    def test_uses_none_if_no_token_supplied_and_no_github_token_defined_as_environment_variable(self):
+        with patch.object(sys, 'argv', ['pip-install', 'requirements.txt']):
+            install()
+
+        self.mock_collect.assert_called_once_with('requirements.txt',
+                                                  transform_with_token=None)
+
     def test_commandline_requires_requirements_file(self):
         with patch('sys.stderr', new_callable=StringIO):
             with patch.object(sys, 'argv', ['pip-install']):

Environment variable GITHUB_TOKEN is ignored
If `--token` isn't provided on invocation while environment variable `GITHUB_TOKEN` is defined, the environment variable's value should be used as the access token.
tests/unit/test_commandline.py::TestCommandLine::test_uses_github_token_environment_variable_if_no_token_supplied
tests/unit/test_commandline.py::TestCommandLine::test_calls_pip_with_install_and_collected_requirements tests/unit/test_commandline.py::TestCommandLine::test_raises_error_if_pip_fails tests/unit/test_commandline.py::TestCommandLine::test_commandline_passes_requirements_file_to_collect tests/unit/test_commandline.py::TestCommandLine::test_commandline_requires_requirements_file tests/unit/test_commandline.py::TestCommandLine::test_commandline_passes_specified_token_to_collect tests/unit/test_commandline.py::TestCommandLine::test_uses_none_if_no_token_supplied_and_no_github_token_defined_as_environment_variable