diff --git a/requirements.txt b/requirements.txt
index 96394ae..ff534dd 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,3 +5,4 @@ singularity==3.0.0
 jinja2==3.0.1
 networkx
 tabulate<0.9.0
+pulp < 2.8