diff --git a/blacklist.txt b/blacklist.txt
index c0a4d1de3a..695bb9eec1 100644
--- a/blacklist.txt
+++ b/blacklist.txt
@@ -18,10 +18,9 @@ pycodestyle
 pylint
 yamllint
 
-# The following horizon and Neutron libraries need to be blacklisted
+# The following Neutron libraries need to be blacklisted
 # as they do not use cycle-with-intermediary.  The only time they
 # would be updated is at release time.
-horizon
 networking-bagpipe
 networking-bgpvpn
 networking-l2gw
diff --git a/upper-constraints.txt b/upper-constraints.txt
index b7d8070f0a..84888614de 100644
--- a/upper-constraints.txt
+++ b/upper-constraints.txt
@@ -567,3 +567,4 @@ sysv-ipc===1.0.1
 sphinxcontrib-applehelp===1.0.2
 scikit-learn===0.24.0
 setuptools===51.1.2
+horizon===19.0.0