diff --git a/cpp/graph_ccm.hpp b/cpp/graph_ccm.hpp
index e9844e398e31ed5f4f0b8c75f384c5375239951c..722389df1d432543e97ffd4c026d8af4b2fabd5d 100644
--- a/cpp/graph_ccm.hpp
+++ b/cpp/graph_ccm.hpp
@@ -69,13 +69,13 @@ bool constrainedConfigurationModel(DegreeSequence &ds, Graph &g, RNG &rng,
         if (method2) {
             // Now assign randomly to the remaining vertices
             // weighted by the number of half-edges they have left
-            auto vIter = uIter;
             while (dmax--) {
                 std::uniform_int_distribution<> distr(1, availableEdges);
                 // Go from edge index to number. We should really have a proper
                 // data structure like some cumulative tree
                 unsigned int halfEdge = distr(rng);
                 unsigned int cumulative = 0;
+                auto vIter = uIter;
                 for (auto iter = available.begin(); iter != available.end();
                      ++iter) {
                     cumulative += iter->first;
@@ -115,11 +115,13 @@ bool constrainedConfigurationModel(DegreeSequence &ds, Graph &g, RNG &rng,
                     break;
                 }
             }
+            if (vIter == uIter)
+                std::cerr << "ERROR 4 in CCM2.\n";
             // pair u to v
             if (vIter->first == 0)
-                std::cerr << "ERROR 4 in CCM1.\n";
+                std::cerr << "ERROR 5 in CCM1.\n";
             if (!g.addEdge({u, vIter->second}))
-                std::cerr << "ERROR 5. Could not add edge in CCM1.\n";
+                std::cerr << "ERROR 6. Could not add edge in CCM1.\n";
             // Purge anything with degree zero
             // Be careful with invalidating the other iterator!
             // Degree of u is always greater or equal to the degree of v