diff --git a/build/tools/before_install.sh b/build/tools/before_install.sh
index f8b4c59658..6a5634bcef 100755
--- a/build/tools/before_install.sh
+++ b/build/tools/before_install.sh
@@ -17,7 +17,7 @@ case $(uname -s) in
                 # Enable the `-dbgsym` repositories.
                 echo "deb http://ddebs.ubuntu.com ${codename} main restricted universe multiverse
                 deb http://ddebs.ubuntu.com ${codename}-updates main restricted universe multiverse" | \
-                $SUDO tee --append /etc/apt/sources.list.d/ddebs.list
+                $SUDO tee --append /etc/apt/sources.list.d/ddebs.list >/dev/null
 
                 # Import the debug symbol archive signing key from the Ubuntu server.
                 # Note that this command works only on Ubuntu 18.04 LTS and newer.