diff --git a/requirements.txt b/requirements.txt
index 562573f..5ab0f51 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -11,3 +11,4 @@ stix2==3.0.1
 stix2-patterns==1.3.2
 pyopenssl
 beautifulsoup4
+pyasn1