diff --git a/spack.yaml b/spack.yaml
index c8f6a353e8e3a9cf4fc4e15ae888967f16753a6e..7189743f387452e832c900aefabd75d6aaeb9f64 100644
--- a/spack.yaml
+++ b/spack.yaml
@@ -46,6 +46,7 @@ spack:
     local_something: /builds/akarmas/ebrains-spack-builds/jobs_scratch_dir/local_mirror
     # some random cache :p (build_cache/ gets added)
     hacky_cache: https://brainscales-r.kip.uni-heidelberg.de:7443/nmpi/tmp
+    public_mirror: https://spack-llnl-mirror.s3-us-west-2.amazonaws.com/
 
   gitlab-ci:
     bootstrap: