diff --git a/formulate/version.py b/formulate/version.py
index 7ee5887..504e799 100644
--- a/formulate/version.py
+++ b/formulate/version.py
@@ -11,6 +11,6 @@
 ]
 
 
-__version__ = '0.0.5'
+__version__ = '0.0.6'
 version = __version__
 version_info = __version__.split('.')
diff --git a/setup.py b/setup.py
index 933e487..6f0da00 100644
--- a/setup.py
+++ b/setup.py
@@ -5,7 +5,6 @@
 from __future__ import print_function
 
 import os.path
-import sys
 
 from setuptools import find_packages
 from setuptools import setup
@@ -32,7 +31,7 @@ def get_version():
       download_url='https://github.com/scikit-hep/formulate/releases',
       license='BSD 3-clause',
       test_suite='tests',
-      install_requires=['numpy', 'pyparsing', 'colorlog', 'aenum', 'scipy'],
+      install_requires=['numpy', 'pyparsing>=2.1.9', 'colorlog', 'aenum', 'scipy'],
       setup_requires=['pytest-runner'],
       tests_require=['pytest'],
       classifiers=[