diff --git a/requirements_build_linux.txt b/requirements_build_linux.txt
index 974e9fd75..3a4640baf 100644
--- a/requirements_build_linux.txt
+++ b/requirements_build_linux.txt
@@ -1,8 +1,8 @@
-PyInstaller	>= 3.2.1
+PyInstaller >= 3.2.1
 cycler >= 0.10.0
 functools32 >= 3.2.3
 future >= 0.16.0
 numpy >= 1.12.
 pyparsing >= 2.1.10
 pytz >= 2016.10
-six >= 1.10.0
+six
diff --git a/requirements_build_windows.txt b/requirements_build_windows.txt
index 51f6135fd..173ce92d0 100644
--- a/requirements_build_windows.txt
+++ b/requirements_build_windows.txt
@@ -7,3 +7,4 @@ pyparsing >= 2.1.10
 pypiwin32 >= 219
 pytz >= 2016.10
 six >= 1.10.0
+tornado