diff --git a/lib/spack/spack/solver/concretize.lp b/lib/spack/spack/solver/concretize.lp
index 341b57d6102..880851cd59f 100644
--- a/lib/spack/spack/solver/concretize.lp
+++ b/lib/spack/spack/solver/concretize.lp
@@ -1142,6 +1142,7 @@ depth(Package, N + 1) :-
         max_depth - 1
     },
     N = 0..max_depth - 1,
+    not attr("root", Package),
     attr("node", Package).