diff --git a/pytest_variables/__init__.py b/pytest_variables/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/pytest_variables/errors.py b/pytest_variables/errors.py
new file mode 100644
index 0000000..4b8e0d9
--- /dev/null
+++ b/pytest_variables/errors.py
@@ -0,0 +1,8 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+class ValueError(Exception):
+    """pytest-variables usage error."""
+    pass
diff --git a/pytest_variables.py b/pytest_variables/plugin.py
similarity index 68%
rename from pytest_variables.py
rename to pytest_variables/plugin.py
index 9ebf9f5..6f07335 100644
--- a/pytest_variables.py
+++ b/pytest_variables/plugin.py
@@ -4,8 +4,11 @@
 
 import os.path
 import sys
+
 import pytest
 
+from pytest_variables import errors
+
 
 def default(module, path):
     return module.load(path)
@@ -38,18 +41,27 @@ def pytest_addoption(parser):
         help='path to variables file.')
 
 
-@pytest.fixture(scope='session')
-def variables(request):
-    """Provide test variables from a specified file"""
-    data = {}
-    for path in request.config.getoption('variables'):
+def pytest_configure(config):
+    config._variables = {}
+    for path in config.getoption('variables'):
         ext = os.path.splitext(path)[1][1:].lower() or 'json'
         with open(path) as f:
             try:
-                data.update(import_parser(f, *parser_table[ext]))
-            except (TypeError, KeyError, ValueError):
+                variables = import_parser(f, *parser_table[ext])
+                print(variables)
+                config._variables.update(variables)
+            except KeyError:
                 print("Could not find a parser for the file extension '{0}'. "
                       'Supported extensions are: {1}'.format(
                           ext, ', '.join(sorted(parser_table.keys()))))
-                data.update(import_parser(f, *parser_table['json']))
-    return data
+                config._variables.update(
+                    import_parser(f, *parser_table['json']))
+            except ValueError as e:
+                raise errors.ValueError('Unable to parse {0}: {1}'.format(
+                    path, e))
+
+
+@pytest.fixture(scope='session')
+def variables(pytestconfig):
+    """Provide test variables from a specified file"""
+    return pytestconfig._variables
diff --git a/setup.py b/setup.py
index 441973f..4a7795c 100644
--- a/setup.py
+++ b/setup.py
@@ -7,8 +7,8 @@
       author='Dave Hunt',
       author_email='dhunt@mozilla.com',
       url='https://github.com/pytest-dev/pytest-variables',
-      py_modules=['pytest_variables'],
-      entry_points={'pytest11': ['variables = pytest_variables']},
+      packages=['pytest_variables'],
+      entry_points={'pytest11': ['variables = pytest_variables.plugin']},
       install_requires=['pytest>=2.4.2'],
       extras_require={
           'hjson': ['hjson'],
diff --git a/test_variables.py b/test_variables.py
index 3006479..3f74513 100644
--- a/test_variables.py
+++ b/test_variables.py
@@ -14,17 +14,17 @@ def pytest_generate_tests(metafunc):
         metafunc.parametrize('file_format', ['json', 'hjson', 'yaml'])
 
 
-def run(testdir, file_format='json', variables=None):
+def run(testdir, file_format='json', variables=None, raw=False):
     variables = variables or [{"foo": "bar"}]
     args = []
     for i, v in enumerate(variables):
-        if file_format == 'hjson':
+        if file_format == 'hjson' and not raw:
             hjson = pytest.importorskip('hjson')
             v = hjson.dumps(v)
-        elif file_format == 'yaml':
+        elif file_format == 'yaml' and not raw:
             yaml = pytest.importorskip('yaml')
             v = yaml.dump(v)
-        else:
+        elif not raw:
             import json
             v = json.dumps(v)
         args.append('--variables')
@@ -75,12 +75,9 @@ def test(variables):
 
 def test_invalid_format(testdir, file_format):
     testdir.makepyfile('def test(variables): pass')
-    result = run(testdir, file_format, ['invalid'])
-    assert result.ret == 1
-    if sys.version_info < (3, 5, 0):
-        result.stdout.fnmatch_lines(['*ValueError: *'])
-    else:
-        result.stdout.fnmatch_lines(['*JSONDecodeError: *'])
+    result = run(testdir, file_format, ['invalid'], raw=True)
+    assert result.ret == 3
+    result.stderr.fnmatch_lines(['*ValueError: Unable to parse*'])
 
 
 def test_key_error(testdir, file_format):