diff --git a/nixos/modules/services/databases/mongodb.nix b/nixos/modules/services/databases/mongodb.nix
index 4453a182990d..4af0b9d44e13 100644
--- a/nixos/modules/services/databases/mongodb.nix
+++ b/nixos/modules/services/databases/mongodb.nix
@@ -176,7 +176,7 @@ in
         postStart = ''
             if test -e "${cfg.dbpath}/.first_startup"; then
               ${optionalString (cfg.initialScript != null) ''
-                ${mongodb}/bin/mongo -u root -p ${cfg.initialRootPassword} admin "${cfg.initialScript}"
+                ${mongodb}/bin/mongo ${optionalString (cfg.enableAuth) "-u root -p ${cfg.initialRootPassword}"} admin "${cfg.initialScript}"
               ''}
               rm -f "${cfg.dbpath}/.first_startup"
             fi