diff --git a/companion.txt b/companion.txt
index 769c574d315..b2e16a7e93d 100644
--- a/companion.txt
+++ b/companion.txt
@@ -18,6 +18,7 @@ https://github.com/willvousden/ptemcee/archive/master.tar.gz
 --extra-index-url https://download.pytorch.org/whl/cpu
 torch
 nessai>=0.11.0
+pypmc==1.2.2
 snowline
 
 # useful to look at PyCBC Live with htop