diff --git a/optional_requirements.txt b/optional_requirements.txt
index c002738f5c87d5ff8f6533c0f94ae2f857d3df96..ea820151245ce3baa891132d4463cc5ff0d3db16 100644
--- a/optional_requirements.txt
+++ b/optional_requirements.txt
@@ -1,4 +1,5 @@
 astropy
 lalsuite<=6.48.1.dev20180823
 gwpy
-theano
\ No newline at end of file
+theano
+cpnest
\ No newline at end of file