diff --git a/setup.py b/setup.py
index a3c44866..51563398 100644
--- a/setup.py
+++ b/setup.py
@@ -60,7 +60,8 @@ setup(
                        '*.h', '*.cpp', '*.bash', '*.txt',
                        '*.dll', '*.lib', '*.so', '*.pyd',
                        '*.dat', '*.ini', '*.pfx', '*.scc', '*.crt', '*.key']},
+    install_requires=['six>=1.11.0'],
     extras_require={
         'tq': ["tornado>=4.5.1", "sortedcontainers>=1.5.7"],
     }
-)
\ No newline at end of file
+)