diff --git a/nixos/modules/services/web-apps/discourse.nix b/nixos/modules/services/web-apps/discourse.nix
index ba5989800ea..49958fc6190 100644
--- a/nixos/modules/services/web-apps/discourse.nix
+++ b/nixos/modules/services/web-apps/discourse.nix
@@ -5,11 +5,16 @@ let
 
   cfg = config.services.discourse;
 
+  # Keep in sync with https://github.com/discourse/discourse_docker/blob/master/image/base/Dockerfile#L5
+  upstreamPostgresqlVersion = lib.getVersion pkgs.postgresql_13;
+
   postgresqlPackage = if config.services.postgresql.enable then
                         config.services.postgresql.package
                       else
                         pkgs.postgresql;
 
+  postgresqlVersion = lib.getVersion postgresqlPackage;
+
   # We only want to create a database if we're actually going to connect to it.
   databaseActuallyCreateLocally = cfg.database.createLocally && cfg.database.host == null;
 
@@ -263,6 +268,17 @@ in
             Discourse database user.
           '';
         };
+
+        ignorePostgresqlVersion = lib.mkOption {
+          type = lib.types.bool;
+          default = false;
+          description = ''
+            Whether to allow other versions of PostgreSQL than the
+            recommended one. Only effective when
+            <option>services.discourse.database.createLocally</option>
+            is enabled.
+          '';
+        };
       };
 
       redis = {
@@ -505,6 +521,12 @@ in
         assertion = cfg.hostname != "";
         message = "Could not automatically determine hostname, set service.discourse.hostname manually.";
       }
+      {
+        assertion = cfg.database.ignorePostgresqlVersion || (databaseActuallyCreateLocally -> upstreamPostgresqlVersion == postgresqlVersion);
+        message = "The PostgreSQL version recommended for use with Discourse is ${upstreamPostgresqlVersion}, you're using ${postgresqlVersion}. "
+                  + "Either update your PostgreSQL package to the correct version or set services.discourse.database.ignorePostgresqlVersion. "
+                  + "See https://nixos.org/manual/nixos/stable/index.html#module-postgresql for details on how to upgrade PostgreSQL.";
+      }
     ];
 
 
diff --git a/nixos/tests/discourse.nix b/nixos/tests/discourse.nix
index 3c965550fe0..2ed6fb957c2 100644
--- a/nixos/tests/discourse.nix
+++ b/nixos/tests/discourse.nix
@@ -51,6 +51,8 @@ import ./make-test-python.nix (
 
         environment.systemPackages = [ pkgs.jq ];
 
+        services.postgresql.package = pkgs.postgresql_13;
+
         services.discourse = {
           enable = true;
           inherit admin;