diff --git a/nixos/modules/services/databases/postgresql.nix b/nixos/modules/services/databases/postgresql.nix
index 87b236dd5fd..5661edbee2d 100644
--- a/nixos/modules/services/databases/postgresql.nix
+++ b/nixos/modules/services/databases/postgresql.nix
@@ -105,6 +105,80 @@ in
         '';
       };
 
+      ensureDatabases = mkOption {
+        type = types.listOf types.str;
+        default = [];
+        description = ''
+          Ensures that the specified databases exist.
+          This option will never delete existing databases, especially not when the value of this
+          option is changed. This means that databases created once through this option or
+          otherwise have to be removed manually.
+        '';
+        example = [
+          "gitea"
+          "nextcloud"
+        ];
+      };
+
+      ensureUsers = mkOption {
+        type = types.listOf (types.submodule {
+          options = {
+            name = mkOption {
+              type = types.str;
+              description = ''
+                Name of the user to ensure.
+              '';
+            };
+            ensurePermissions = mkOption {
+              type = types.attrsOf types.str;
+              default = {};
+              description = ''
+                Permissions to ensure for the user, specified as an attribute set.
+                The attribute names specify the database and tables to grant the permissions for.
+                The attribute values specify the permissions to grant. You may specify one or
+                multiple comma-separated SQL privileges here.
+
+                For more information on how to specify the target
+                and on which privileges exist, see the
+                <link xlink:href="https://www.postgresql.org/docs/current/sql-grant.html">GRANT syntax</link>.
+                The attributes are used as <code>GRANT ''${attrName} ON ''${attrValue}</code>.
+              '';
+              example = literalExample ''
+                {
+                  "DATABASE nextcloud" = "ALL PRIVILEGES";
+                  "ALL TABLES IN SCHEMA public" = "ALL PRIVILEGES";
+                }
+              '';
+            };
+          };
+        });
+        default = [];
+        description = ''
+          Ensures that the specified users exist and have at least the ensured permissions.
+          The PostgreSQL users will be identified using peer authentication. This authenticates the Unix user with the
+          same name only, and that without the need for a password.
+          This option will never delete existing users or remove permissions, especially not when the value of this
+          option is changed. This means that users created and permissions assigned once through this option or
+          otherwise have to be removed manually.
+        '';
+        example = literalExample ''
+          [
+            {
+              name = "nextcloud";
+              ensurePermissions = {
+                "DATABASE nextcloud" = "ALL PRIVILEGES";
+              };
+            }
+            {
+              name = "superuser";
+              ensurePermissions = {
+                "ALL TABLES IN SCHEMA public" = "ALL PRIVILEGES";
+              };
+            }
+          ]
+        '';
+      };
+
       enableTCPIP = mkOption {
         type = types.bool;
         default = false;
@@ -256,17 +330,30 @@ in
         # Wait for PostgreSQL to be ready to accept connections.
         postStart =
           ''
-            while ! ${pkgs.sudo}/bin/sudo -u ${cfg.superUser} psql --port=${toString cfg.port} -d postgres -c "" 2> /dev/null; do
+            PSQL="${pkgs.sudo}/bin/sudo -u ${cfg.superUser} psql --port=${toString cfg.port}"
+
+            while ! $PSQL -d postgres -c "" 2> /dev/null; do
                 if ! kill -0 "$MAINPID"; then exit 1; fi
                 sleep 0.1
             done
 
             if test -e "${cfg.dataDir}/.first_startup"; then
               ${optionalString (cfg.initialScript != null) ''
-                ${pkgs.sudo}/bin/sudo -u ${cfg.superUser} psql -f "${cfg.initialScript}" --port=${toString cfg.port} -d postgres
+                $PSQL -f "${cfg.initialScript}" -d postgres
               ''}
               rm -f "${cfg.dataDir}/.first_startup"
             fi
+          '' + optionalString (cfg.ensureDatabases != []) ''
+            ${concatMapStrings (database: ''
+              $PSQL -tAc "SELECT 1 FROM pg_database WHERE datname = '${database}'" | grep -q 1 || $PSQL -tAc "CREATE DATABASE ${database}"
+            '') cfg.ensureDatabases}
+          '' + ''
+            ${concatMapStrings (user: ''
+              $PSQL -tAc "SELECT 1 FROM pg_roles WHERE rolname='${user.name}'" | grep -q 1 || $PSQL -tAc "CREATE USER ${user.name}"
+              ${concatStringsSep "\n" (mapAttrsToList (database: permission: ''
+                $PSQL -tAc "GRANT ${permission} ON ${database} TO ${user.name}"
+              '') user.ensurePermissions)}
+            '') cfg.ensureUsers}
           '';
 
         unitConfig.RequiresMountsFor = "${cfg.dataDir}";
diff --git a/nixos/tests/redmine.nix b/nixos/tests/redmine.nix
index ea72a0121d1..cbdb5c8d295 100644
--- a/nixos/tests/redmine.nix
+++ b/nixos/tests/redmine.nix
@@ -7,7 +7,7 @@ with import ../lib/testing.nix { inherit system pkgs; };
 with pkgs.lib;
 
 let
-  redmineTest = package: makeTest {
+  mysqlTest = package: makeTest {
     machine =
       { config, pkgs, ... }:
       { services.mysql.enable = true;
@@ -21,6 +21,7 @@ let
 
         services.redmine.enable = true;
         services.redmine.package = package;
+        services.redmine.database.type = "mysql2";
         services.redmine.database.socket = "/run/mysqld/mysqld.sock";
         services.redmine.plugins = {
           redmine_env_auth = pkgs.fetchurl {
@@ -38,7 +39,44 @@ let
 
     testScript = ''
       startAll;
+      $machine->waitForUnit('redmine.service');
+      $machine->waitForOpenPort('3000');
+      $machine->succeed("curl --fail http://localhost:3000/");
+    '';
+  };
 
+  pgsqlTest = package: makeTest {
+    machine =
+      { config, pkgs, ... }:
+      { services.postgresql.enable = true;
+        services.postgresql.ensureDatabases = [ "redmine" ];
+        services.postgresql.ensureUsers = [
+          { name = "redmine";
+            ensurePermissions = { "DATABASE redmine" = "ALL PRIVILEGES"; };
+          }
+        ];
+
+        services.redmine.enable = true;
+        services.redmine.package = package;
+        services.redmine.database.type = "postgresql";
+        services.redmine.database.host = "";
+        services.redmine.database.port = 5432;
+        services.redmine.plugins = {
+          redmine_env_auth = pkgs.fetchurl {
+            url = https://github.com/Intera/redmine_env_auth/archive/0.7.zip;
+            sha256 = "1xb8lyarc7mpi86yflnlgyllh9hfwb9z304f19dx409gqpia99sc";
+          };
+        };
+        services.redmine.themes = {
+          dkuk-redmine_alex_skin = pkgs.fetchurl {
+            url = https://bitbucket.org/dkuk/redmine_alex_skin/get/1842ef675ef3.zip;
+            sha256 = "0hrin9lzyi50k4w2bd2b30vrf1i4fi1c0gyas5801wn8i7kpm9yl";
+          };
+        };
+      };
+
+    testScript = ''
+      startAll;
       $machine->waitForUnit('redmine.service');
       $machine->waitForOpenPort('3000');
       $machine->succeed("curl --fail http://localhost:3000/");
@@ -46,13 +84,18 @@ let
   };
 in
 {
-  redmine_3 = redmineTest pkgs.redmine // {
-    name = "redmine_3";
+  v3-mysql = mysqlTest pkgs.redmine // {
+    name = "v3-mysql";
     meta.maintainers = [ maintainers.aanderse ];
   };
 
-  redmine_4 = redmineTest pkgs.redmine_4 // {
-    name = "redmine_4";
+  v4-mysql = mysqlTest pkgs.redmine_4 // {
+    name = "v4-mysql";
+    meta.maintainers = [ maintainers.aanderse ];
+  };
+
+  v4-pgsql = pgsqlTest pkgs.redmine_4 // {
+    name = "v4-pgsql";
     meta.maintainers = [ maintainers.aanderse ];
   };
 }