diff --git a/Dockerfile.buster b/Dockerfile.buster
index 96c8f66e27a8967d04f5683ef824f2bd206352b5..f77a0f1b8a5a7ec70e5724fb755749b2c7223747 100644
--- a/Dockerfile.buster
+++ b/Dockerfile.buster
@@ -3,7 +3,7 @@ FROM debian:buster AS uffd-base
 RUN apt-get -qq update && \
     apt-get -qq dist-upgrade && \
     apt-get -qq install sqlite3 locales-all git python3 python3-coverage python3-ldap3 python3-flask python3-flask-sqlalchemy lsb-release python3-pip && \
-    pip3 install pylint --upgrade && \
+    pip3 install pylint html5validator --upgrade && \
     apt-get -qq clean
 
 FROM uffd-base AS openldap-base