diff --git a/spack.yaml b/spack.yaml
index 9f97800e61a36d9acd4346f82952e6f018df7d86..c507f2e320ef05496dcc0cb611d2c2645f86be3f 100644
--- a/spack.yaml
+++ b/spack.yaml
@@ -68,4 +68,5 @@ spack:
     #- sda
     # demo for codejam12
     #- funniest1022
-  concretization: together
+  concretizer:
+    unify: true