diff --git a/requirements.txt b/requirements.txt
index abb48da..fc5679a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,10 +3,12 @@ attrs==24.2.0
 bibtexparser==1.4.2
 certifi==2024.8.30
 charset-normalizer==3.3.2
+citeproc-py==0.6.0
 feedparser==6.0.11
 ics==0.7.2
 idna==3.10
 Jinja2==3.1.4
+lxml==5.3.0
 Markdown==3.7
 MarkupSafe==2.1.5
 pyparsing==3.1.4