diff --git a/lib/spack/spack/solver/concretize.lp b/lib/spack/spack/solver/concretize.lp
index fc725a81be..094992aaf0 100644
--- a/lib/spack/spack/solver/concretize.lp
+++ b/lib/spack/spack/solver/concretize.lp
@@ -101,13 +101,14 @@ unification_set(SetID, VirtualNode) :- provider(PackageNode, VirtualNode), unifi
 
 % TODO: literals, at the moment, can only influence the "root" unification set. This needs to be extended later.
 
-special_case("node_flag_source").
-special_case("depends_on").
+% Node attributes that have multiple node arguments (usually, only the first argument is a node)
+multiple_nodes_attribute("node_flag_source").
+multiple_nodes_attribute("depends_on").
 
 % Map constraint on the literal ID to facts on the node
 attr(Name, node(root_node_id, A1))             :- literal(LiteralID, Name, A1), solve_literal(LiteralID).
 attr(Name, node(root_node_id, A1), A2)         :- literal(LiteralID, Name, A1, A2), solve_literal(LiteralID).
-attr(Name, node(root_node_id, A1), A2, A3)     :- literal(LiteralID, Name, A1, A2, A3), solve_literal(LiteralID), not special_case(Name).
+attr(Name, node(root_node_id, A1), A2, A3)     :- literal(LiteralID, Name, A1, A2, A3), solve_literal(LiteralID), not multiple_nodes_attribute(Name).
 attr(Name, node(root_node_id, A1), A2, A3, A4) :- literal(LiteralID, Name, A1, A2, A3, A4), solve_literal(LiteralID).
 
 % Special cases where nodes occur in arguments other than A1
@@ -302,7 +303,7 @@ trigger_condition_holds(ID, RequestorNode) :-
   trigger_node(ID, PackageNode, RequestorNode);
   attr(Name, node(X, A1))             : condition_requirement(ID, Name, A1),             condition_nodes(ID, PackageNode, node(X, A1));
   attr(Name, node(X, A1), A2)         : condition_requirement(ID, Name, A1, A2),         condition_nodes(ID, PackageNode, node(X, A1));
-  attr(Name, node(X, A1), A2, A3)     : condition_requirement(ID, Name, A1, A2, A3),     condition_nodes(ID, PackageNode, node(X, A1)), not special_case(Name);
+  attr(Name, node(X, A1), A2, A3)     : condition_requirement(ID, Name, A1, A2, A3),     condition_nodes(ID, PackageNode, node(X, A1)), not multiple_nodes_attribute(Name);
   attr(Name, node(X, A1), A2, A3, A4) : condition_requirement(ID, Name, A1, A2, A3, A4), condition_nodes(ID, PackageNode, node(X, A1));
   % Special cases
   attr("node_flag_source", node(X, A1), A2, node(Y, A3)) : condition_requirement(ID, "node_flag_source", A1, A2, A3), condition_nodes(ID, PackageNode, node(X, A1)), condition_nodes(ID, PackageNode, node(Y, A3));
@@ -348,7 +349,7 @@ imposed_nodes(ConditionID, PackageNode, node(X, A1))
 % Conditions that hold impose may impose constraints on other specs
 attr(Name, node(X, A1))             :- impose(ID, PackageNode), imposed_constraint(ID, Name, A1),             imposed_nodes(ID, PackageNode, node(X, A1)).
 attr(Name, node(X, A1), A2)         :- impose(ID, PackageNode), imposed_constraint(ID, Name, A1, A2),         imposed_nodes(ID, PackageNode, node(X, A1)).
-attr(Name, node(X, A1), A2, A3)     :- impose(ID, PackageNode), imposed_constraint(ID, Name, A1, A2, A3),     imposed_nodes(ID, PackageNode, node(X, A1)), not special_case(Name).
+attr(Name, node(X, A1), A2, A3)     :- impose(ID, PackageNode), imposed_constraint(ID, Name, A1, A2, A3),     imposed_nodes(ID, PackageNode, node(X, A1)), not multiple_nodes_attribute(Name).
 attr(Name, node(X, A1), A2, A3, A4) :- impose(ID, PackageNode), imposed_constraint(ID, Name, A1, A2, A3, A4), imposed_nodes(ID, PackageNode, node(X, A1)).
 
 % For node flag sources we need to look at the condition_set of the source, since it is the dependent