diff --git a/requirements.txt b/requirements.txt
index 3f53ad8..bdf3045 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,6 @@
 numpy==1.9.2
+--allow-external gnuplot-py
+--allow-unverified gnuplot-py
 gnuplot-py==1.8
 Pint==0.5.1
 PyModelFit==0.1.2