diff --git a/lib/spack/spack/solver/concretize.lp b/lib/spack/spack/solver/concretize.lp
index b7acbdce21..836c76fe30 100644
--- a/lib/spack/spack/solver/concretize.lp
+++ b/lib/spack/spack/solver/concretize.lp
@@ -1128,8 +1128,11 @@ target_weight(Target, 0)
 node_target_weight(PackageNode, MinWeight)
  :- attr("node", PackageNode),
     attr("node_target", PackageNode, Target),
+    target(Target),
     MinWeight = #min { Weight : target_weight(Target, Weight) }.
 
+:- attr("node_target", PackageNode, Target), not node_target_weight(PackageNode, _).
+
 % compatibility rules for targets among nodes
 node_target_match(ParentNode, DependencyNode)
   :- attr("depends_on", ParentNode, DependencyNode, Type), Type != "build",