diff --git a/lib/spack/docs/configuration.rst b/lib/spack/docs/configuration.rst
index b2e81e4334..22eff77655 100644
--- a/lib/spack/docs/configuration.rst
+++ b/lib/spack/docs/configuration.rst
@@ -53,6 +53,7 @@ in the first directory it finds to which it has write access.  Add
 more elements to the list to indicate where your own site's temporary
 directory is.
 
+.. _sec-external_packages:
 
 External Packages
 ----------------------------