diff --git a/scripts/lib/upgrade-zulip-stage-2 b/scripts/lib/upgrade-zulip-stage-2
index d5b724ab55..06ffe6964f 100755
--- a/scripts/lib/upgrade-zulip-stage-2
+++ b/scripts/lib/upgrade-zulip-stage-2
@@ -160,6 +160,12 @@ if not args.skip_puppet:
     subprocess.check_call(["apt-get", "update"])
     subprocess.check_call(["apt-get", "-y", "upgrade"])
 
+# To bootstrap zulip-puppet-apply, we need to install the system yaml
+# package; new installs get this, but old installs may not have it.
+if not os.path.exists("/usr/share/doc/python3-yaml"):
+    logging.info("Installing system YAML package, for puppet...")
+    subprocess.check_call(["apt-get", "install", "python3-yaml"])
+
 if not os.path.exists(os.path.join(deploy_path, "zproject/prod_settings.py")):
     # This is normally done in unpack-zulip, but for upgrading from
     # zulip<1.4.0, we need to do it.  See discussion in commit 586b23637.