diff --git a/lemon/capacity_scaling.h b/lemon/capacity_scaling.h
--- a/lemon/capacity_scaling.h
+++ b/lemon/capacity_scaling.h
@@ -681,7 +681,7 @@
 
     // Initialize the algorithm
     ProblemType init() {
-      if (_node_num == 0) return INFEASIBLE;
+      if (_node_num <= 1) return INFEASIBLE;
 
       // Check the sum of supply values
       _sum_supply = 0;
diff --git a/lemon/cost_scaling.h b/lemon/cost_scaling.h
--- a/lemon/cost_scaling.h
+++ b/lemon/cost_scaling.h
@@ -712,7 +712,7 @@
 
     // Initialize the algorithm
     ProblemType init() {
-      if (_res_node_num == 0) return INFEASIBLE;
+      if (_res_node_num <= 1) return INFEASIBLE;
 
       // Check the sum of supply values
       _sum_supply = 0;