diff --git a/requirements-dev.txt b/requirements-dev.txt
index 26090747..804a075c 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,3 +1,4 @@
 pytest
 flake8
-hypothesis
\ No newline at end of file
+hypothesis
+six
\ No newline at end of file