diff --git a/requirements.txt b/requirements.txt
index 9b7e3ce..6fbcc07 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,5 @@
 requests
-biopython>=1.77
+biopython>=1.77,<=1.81
 cachetools<4
 click>=6.7
 wrapt