diff --git a/defaults/nextcloud/default.nix b/defaults/nextcloud/default.nix
index db21a58..11f52c7 100644
--- a/defaults/nextcloud/default.nix
+++ b/defaults/nextcloud/default.nix
@@ -13,7 +13,7 @@
     owner = name;
   };
 
-  qois.postgresql.enable = true;
+  services.postgresql.enable = true;
   qois.backup-client.includePaths = [ config.services.nextcloud.home ];
 
   services.nextcloud = {
diff --git a/nixos-configurations/lindberg-build/applications/attic.nix b/nixos-configurations/lindberg-build/applications/attic.nix
index c0b0cc0..05f65a4 100644
--- a/nixos-configurations/lindberg-build/applications/attic.nix
+++ b/nixos-configurations/lindberg-build/applications/attic.nix
@@ -52,11 +52,10 @@ in
 
   imports = [ ../../../defaults/webserver ];
 
-  qois.postgresql.enable = true;
-
   # Note: Attic cache availability is "best effort", so no artifacts are backed up.
 
   services.postgresql = {
+    enable = true;
     ensureDatabases = [ "atticd" ];
     ensureUsers = [
       {
diff --git a/nixos-configurations/lindberg-build/applications/default.nix b/nixos-configurations/lindberg-build/applications/default.nix
index d634828..d38f4f0 100644
--- a/nixos-configurations/lindberg-build/applications/default.nix
+++ b/nixos-configurations/lindberg-build/applications/default.nix
@@ -7,4 +7,5 @@
   ];
 
   qois.git-ci-runner.enable = true;
+  qois.postgresql.package = pkgs.postgresql_15;
 }
diff --git a/nixos-configurations/lindberg-nextcloud/applications/cloud.nix b/nixos-configurations/lindberg-nextcloud/applications/cloud.nix
index 86716d2..8e6b4ff 100644
--- a/nixos-configurations/lindberg-nextcloud/applications/cloud.nix
+++ b/nixos-configurations/lindberg-nextcloud/applications/cloud.nix
@@ -6,7 +6,7 @@ in
 
   imports = [ ../../../defaults/nextcloud ];
 
-  qois.postgresql.enable = true;
+  services.postgresql.enable = true;
 
   services.nextcloud = {
     hostName = host;
diff --git a/nixos-configurations/lindberg-nextcloud/applications/default.nix b/nixos-configurations/lindberg-nextcloud/applications/default.nix
index 6188fc9..d872c18 100644
--- a/nixos-configurations/lindberg-nextcloud/applications/default.nix
+++ b/nixos-configurations/lindberg-nextcloud/applications/default.nix
@@ -2,4 +2,6 @@
 {
 
   imports = [ ./cloud.nix ];
+
+  qois.postgresql.package = pkgs.postgresql_14;
 }
diff --git a/nixos-configurations/lindberg-webapps/applications/default.nix b/nixos-configurations/lindberg-webapps/applications/default.nix
index c635d21..9efef42 100644
--- a/nixos-configurations/lindberg-webapps/applications/default.nix
+++ b/nixos-configurations/lindberg-webapps/applications/default.nix
@@ -6,4 +6,5 @@
   qois.vault.enable = true;
   qois.git.enable = true;
   qois.static-page.enable = true;
+  qois.postgresql.package = pkgs.postgresql_15;
 }
diff --git a/nixos-modules/postgresql/default.nix b/nixos-modules/postgresql/default.nix
index e2a8e88..b67f574 100644
--- a/nixos-modules/postgresql/default.nix
+++ b/nixos-modules/postgresql/default.nix
@@ -11,11 +11,15 @@ in
 with lib;
 {
   options.qois.postgresql = {
-    enable = mkEnableOption ''Enable postgresql services with defaults'';
+    # Note: this module is auto-enabled if postgres is used.
+    package = mkPackageOption pkgs "postgresql" {
+      example = "postgresql_15";
+      default = null;
+    };
   };
 
-  config = mkIf cfg.enable {
-    services.postgresql.enable = true;
+  config = mkIf config.services.postgresql.enable {
+    services.postgresql.package = cfg.package;
     services.postgresqlBackup.enable = true;
     qois.backup-client.includePaths = [ config.services.postgresqlBackup.location ];
   };
diff --git a/nixos-modules/qois/git/default.nix b/nixos-modules/qois/git/default.nix
index 20ba2dd..2bb34be 100644
--- a/nixos-modules/qois/git/default.nix
+++ b/nixos-modules/qois/git/default.nix
@@ -21,7 +21,7 @@ with lib;
   };
 
   config = mkIf cfg.enable {
-    qois.postgresql.enable = true;
+    services.postgresql.enable = true;
 
     services.forgejo = {
       enable = true;
diff --git a/nixos-modules/vault/default.nix b/nixos-modules/vault/default.nix
index e61b5fe..9676d3d 100644
--- a/nixos-modules/vault/default.nix
+++ b/nixos-modules/vault/default.nix
@@ -48,8 +48,6 @@ with lib;
       };
     };
 
-    qois.postgresql.enable = true;
-
     qois.backup-client.includePaths = [ config.services.vaultwarden.config.DATA_FOLDER ];
 
     services.postgresql =
@@ -57,6 +55,7 @@ with lib;
         name = config.users.users.vaultwarden.name;
       in
       {
+        enable = true;
         ensureUsers = [
           {
             inherit name;