diff --git a/requirements.txt b/requirements.txt
index 68027b5f5..4b1722633 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,6 @@
 # We are currently targeting the versions shipped in Ubuntu 20.04.
 
-tornado==6.4.1  # http://www.tornadoweb.org/en/stable/releases.html
+tornado==5.1.1  # http://www.tornadoweb.org/en/stable/releases.html
 psycopg2==2.9.10  # http://initd.org/psycopg/articles/tag/release/
 sqlalchemy>=1.3,<1.4  # http://docs.sqlalchemy.org/en/latest/changelog/index.html
 netifaces>=0.10,<0.11  # https://bitbucket.org/al45tair/netifaces/src/