diff --git a/setup/system.sh b/setup/system.sh
index 4bc1cfaa..84f6bd89 100755
--- a/setup/system.sh
+++ b/setup/system.sh
@@ -11,12 +11,21 @@ source setup/functions.sh # load our functions
 # text search plugin for (and by) dovecot, which is not available in
 # Ubuntu currently.
 #
-# Add that to the system's list of repositories:
+# Add that to the system's list of repositories using add-apt-repository.
+# But add-apt-repository may not be installed. If it's not available,
+# then install it. But we have to run apt-get update before we try to
+# install anything so the package index is up to date. After adding the
+# PPA, we have to run apt-get update *again* to load the PPA's index,
+# so this must precede the apt-get update line below.
+
+if [ ! -f /usr/bin/add-apt-repository ]; then
+	echo "Installing add-apt-repository..."
+	hide_output apt-get update
+	apt_install software-properties-common
+fi
 
 hide_output add-apt-repository -y ppa:mail-in-a-box/ppa
 
-# The apt-get update in the next step will pull in the PPA's index.
-
 # ### Update Packages
 
 # Update system packages to make sure we have the latest upstream versions of things from Ubuntu.