diff --git a/nixos/modules/services/databases/postgresql.nix b/nixos/modules/services/databases/postgresql.nix
index a83b1a110fed..cc4230d4d6a7 100644
--- a/nixos/modules/services/databases/postgresql.nix
+++ b/nixos/modules/services/databases/postgresql.nix
@@ -190,7 +190,7 @@ in
                 mkdir -m 0700 -p ${cfg.dataDir}
                 if [ "$(id -u)" = 0 ]; then
                   chown -R postgres ${cfg.dataDir}
-                  su -s ${pkgs.stdenv.shell} postgres -c initdb
+                  su -s ${pkgs.stdenv.shell} postgres -c 'initdb -U root'
                 else
                   # For non-root operation.
                   initdb