diff --git a/docs/tutorial_build_automation.rst b/docs/tutorial_build_automation.rst
index c0ba98f031..702243a82f 100644
--- a/docs/tutorial_build_automation.rst
+++ b/docs/tutorial_build_automation.rst
@@ -107,6 +107,10 @@ Here is the test's code:
 
 When :attr:`~reframe.core.pipeline.RegressionTest.build_system` is set to ``'Spack'``, ReFrame will leverage Spack environments in order to build the test code.
 By default, ReFrame will create a new Spack environment in the test's stage directory and add the requested :attr:`~reframe.core.buildsystems.Spack.specs` to it.
+
+.. note::
+   Optional spec attributes, such as ``target`` and ``os``, should be specified in :attr:`~reframe.core.buildsystems.Spack.specs` and not as install options in :attr:`~reframe.core.buildsystems.Spack.install_opts`.
+
 Users may also specify an existing Spack environment by setting the :attr:`~reframe.core.buildsystems.Spack.environment` attribute.
 In this case, ReFrame treats the environment as a *test resource* so it expects to find it under the test's :attr:`~reframe.core.pipeline.RegressionTest.sourcesdir`, which defaults to ``'src'``.