diff --git a/requirements.txt b/requirements.txt
index 12ce5fc6..58f28211 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,7 +1,7 @@
-cython>=0.21
 matplotlib>=1.1.0
 numpy>=1.6.1
 scipy>=0.9
-six>=1.3
+six>=1.4
 networkx>=1.8
 pillow>=1.7.8
+dask[array]>=0.5.0