diff --git a/requirements.txt b/requirements.txt
index 7be8f44..cddb750 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,7 +2,8 @@ cython
 isovar==0.9.0
 mhctools>=1.8.1
 psutil
+pyensembl==1.7.3
 pyyaml
 snakemake==5.4.4
-varcode>=0.8.0
+varcode==0.8.0
 vaxrank==1.0.0