diff --git a/requirements.txt b/requirements.txt
index b3fa94465421ee9996da0d653216f47c2ed24062..0546b93dbabb827ad209c98a3ea9835931a39fe3 100755
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,5 @@
 future
-numpy 
+numpy
 cython
 Pint==0.7.2
 ase==3.12.0
@@ -7,3 +7,4 @@ setuptools
 scipy
 mdtraj==1.7.2
 pandas
+pyyaml