diff --git a/config-hlrs/config.yaml b/config-hlrs/config.yaml
index 7450c75..929aa88 100644
--- a/config-hlrs/config.yaml
+++ b/config-hlrs/config.yaml
@@ -17,6 +17,10 @@ config:
   # Directory where licenses should be located
   license_dir: $spack/../licenses
 
+  # Cache directory for already downloaded source tarballs and archived
+  # repositories. This can be purged with `spack clean --downloads`.
+  source_cache: $user_cache_path/cache
+
 
   # Directory where spack managed environments are created and stored
   environments_root: $spack/../environments