diff --git a/requirements.txt b/requirements.txt
index 40b0d23..e2c6066 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,4 +5,5 @@ PyPDF2==1.20
 elifetools==0.1.7
 coverage==3.7.1
 arrow==0.4.4
-func_timeout==4.3.0
\ No newline at end of file
+func_timeout==4.3.0
+lxml>=4.9.1 # not directly required, pinned by Snyk to avoid a vulnerability
\ No newline at end of file