diff --git a/env/sles15/x86_64/admin/testing/spack.yaml b/env/sles15/x86_64/admin/testing/spack.yaml
index ea17d6d..e75354c 100644
--- a/env/sles15/x86_64/admin/testing/spack.yaml
+++ b/env/sles15/x86_64/admin/testing/spack.yaml
@@ -4,6 +4,8 @@ spack:
   config:
     install_tree:
       root: $spack/opt/spack/testing
+      # Strongly adviced to avoid problems with buildcaches
+      padded_length: 256
   include:
   - $spack/spack-psi/env/$os/$target_family/sysconfigs/packages.yaml
   - $spack/spack-psi/env/$os/$target_family/sysconfigs/compilers.yaml