diff --git a/optimaladj/CausalGraph.py b/optimaladj/CausalGraph.py
index 9450fee..97863e4 100644
--- a/optimaladj/CausalGraph.py
+++ b/optimaladj/CausalGraph.py
@@ -360,7 +360,7 @@ def optimal_adj_set(self, treatment, outcome, L, N):
         H1 = self.build_H1(treatment, outcome, L, N)
         if treatment in H1.neighbors(outcome):
             raise NoAdjException(EXCEPTION_NO_ADJ)
-        elif N == self.nodes() or set(N).issubset(
+        elif set(N) == set(self.nodes()) or set(N).issubset(
             self.ancestors_all(L + [treatment, outcome])
         ):
             optimal = nx.node_boundary(H1, set([outcome]))