diff --git a/lib.nix b/lib.nix
index 275ba4b..9e05c84 100644
--- a/lib.nix
+++ b/lib.nix
@@ -66,13 +66,14 @@ in
       config ? { },
       extra_config ? '''',
       package ? pkgs.postgresql,
-      data_dir ? ".data/",
       port ? 5432,
       listen_addresses ? "localhost",
       ...
     }:
     let
+
       runtimeDir = "${runtime}/${name}";
+      data_dir = "${runtimeDir}/data";
       merged_config =
         (
           if default_config then
@@ -127,7 +128,11 @@ in
           echo
           echo "PostgreSQL is setting up the initial database"
           echo
-          OLDPGHOST="$PGHOST"
+          if [[ -z "$PGHOST" ]]; then
+            OLDPGHOST=""
+          else
+            OLDPGHOST="$PGHOST"
+          fi
           PGHOST=${lib.escapeShellArg runtimeDir}
           pg_ctl -D "${data_dir}" -w start -o "-c unix_socket_directories=${data_dir} -c listen_addresses= -p ${builtins.toString port}"
           pg_ctl -D "${data_dir}" -m fast -w stop