diff --git a/_extras/recommended-practices.md b/_extras/recommended-practices.md
index 6d6dd3c4..3d260afa 100644
--- a/_extras/recommended-practices.md
+++ b/_extras/recommended-practices.md
@@ -63,3 +63,4 @@ For more examples of providing metadata within CWL descriptions, see the [Metada
 [orcid]: https://orcid.org
 [subworkflow]: http://www.commonwl.org/v1.0/Workflow.html#SubworkflowFeatureRequirement
 [metadata-lesson]: /user_guide/17-metadata/
+[spdx]: https://spdx.org/licenses/