diff --git a/puppet/zulip/manifests/base.pp b/puppet/zulip/manifests/base.pp
index 7e4a29d33e..dd9e43557f 100644
--- a/puppet/zulip/manifests/base.pp
+++ b/puppet/zulip/manifests/base.pp
@@ -56,20 +56,7 @@ class zulip::base {
   }
   package { $base_packages: ensure => 'installed' }
 
-  $postgres_version = zulipconf('postgresql', 'version', $release_name ? {
-    'wheezy'  => '9.1',
-    'jessie'  => '9.4',
-    'stretch' => '9.6',
-    'buster'  => '11',
-    'precise' => '9.1',
-    'trusty'  => '9.3',
-    'vivid'   => '9.4',
-    'wily'    => '9.4',
-    'xenial'  => '9.5',
-    'bionic'  => '10',
-    'CentOS7' => '10',
-    'focal'   => '12',
-  })
+  $postgres_version = zulipconf('postgresql', 'version', undef)
 
   $normal_queues = [
     'deferred_work',
diff --git a/scripts/lib/upgrade-zulip-stage-2 b/scripts/lib/upgrade-zulip-stage-2
index 978a179f5e..0e154f6d25 100755
--- a/scripts/lib/upgrade-zulip-stage-2
+++ b/scripts/lib/upgrade-zulip-stage-2
@@ -12,6 +12,10 @@ import os
 import subprocess
 import sys
 import time
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from typing import NoReturn
 
 os.environ["PYTHONUNBUFFERED"] = "y"
 
@@ -27,6 +31,7 @@ from scripts.lib.zulip_tools import (
     get_config,
     get_config_file,
     parse_os_release,
+    set_config,
     su_to_zulip,
 )
 
@@ -36,6 +41,17 @@ logging.Formatter.converter = time.gmtime
 logging.basicConfig(format="%(asctime)s upgrade-zulip-stage-2: %(message)s",
                     level=logging.INFO)
 
+
+def error_desupported_os(vendor: str, os_version: str) -> "NoReturn":
+    # Link to documentation for how to correctly upgrade the OS.
+    logging.critical("Unsupported platform: %s %s", vendor, os_version)
+    logging.info("Sorry! The support for your OS has been discontinued.\n"
+                 "Please upgrade your OS to a supported release first.\n"
+                 "See https://zulip.readthedocs.io/en/latest/production/"
+                 "upgrade-or-modify.html#upgrading-the-operating-system")
+    sys.exit(1)
+
+
 # Do not upgrade on unsupported OS versions.
 UNSUPPORTED_DISTROS = [
     ('ubuntu', '14.04'),
@@ -47,13 +63,7 @@ vendor = distro_info['ID']
 os_version = distro_info['VERSION_ID']
 
 if (vendor, os_version) in UNSUPPORTED_DISTROS:
-    # Link to documentation for how to correctly upgrade the OS.
-    logging.critical("Unsupported platform: %s %s", vendor, os_version)
-    logging.info("Sorry! The support for your OS has been discontinued.\n"
-                 "Please upgrade your OS to a supported release first.\n"
-                 "See https://zulip.readthedocs.io/en/latest/production/"
-                 "upgrade-or-modify.html#upgrading-the-operating-system")
-    sys.exit(1)
+    error_desupported_os(vendor, os_version)
 
 # make sure we have appropriate file permissions
 os.umask(0o22)
@@ -96,6 +106,23 @@ def shutdown_server() -> None:
                           preexec_fn=su_to_zulip)
     IS_SERVER_UP = False
 
+# postgresql.version is required for database servers, but wasn't
+# previously; fill it in based on what the OS provides.
+if os.path.exists('/etc/init.d/postgresql'):
+    postgres_version = get_config(config_file, 'postgresql', 'version')
+    if not postgres_version:
+        default_postgres_version = {
+            ('debian', '10'): '11',
+            ('ubuntu', '18.04'): '10',
+            ('ubuntu', '20.04'): '12',
+            ('centos', '7'): '11',
+        }
+        if (vendor, os_version) in default_postgres_version:
+            postgres_version = default_postgres_version[(vendor, os_version)]
+        else:
+            error_desupported_os(vendor, os_version)
+        set_config(config_file, 'postgresql', 'version', postgres_version)
+
 if glob.glob("/usr/share/postgresql/*/extension/tsearch_extras.control"):
     # Remove legacy tsearch_extras package references
     subprocess.check_call([
diff --git a/scripts/lib/zulip_tools.py b/scripts/lib/zulip_tools.py
index ef4e88a6a5..069e30138d 100755
--- a/scripts/lib/zulip_tools.py
+++ b/scripts/lib/zulip_tools.py
@@ -489,6 +489,16 @@ def get_config(
         return config_file.get(section, key)
     return default_value
 
+def set_config(
+    config_file: configparser.RawConfigParser,
+    section: str,
+    key: str,
+    value: str,
+) -> None:
+    if not config_file.has_section(section):
+        config_file.add_section(section)
+    config_file.set(section, key, value)
+
 def get_config_file() -> configparser.RawConfigParser:
     config_file = configparser.RawConfigParser()
     config_file.read("/etc/zulip/zulip.conf")