diff --git a/src/graph/edge.cc b/src/graph/edge.cc
index 537fd7e80259f17aff19bd50f258e40823be8c65..a304cb248a4ebaf8b3eaa62a7024c2996d09a9d8 100644
--- a/src/graph/edge.cc
+++ b/src/graph/edge.cc
@@ -207,7 +207,7 @@ namespace hpp {
           itpdof2 = itpdof1; ++itpdof2;
           NumericalConstraintPtr_t combination;
           while (itnc2 != nc.end()) {
-            assert (*itnc1 == *itnc2);
+            assert (*itnc1 != *itnc2);
             if (   graph->isComplement (*itnc1, *itnc2, combination)
                 || graph->isComplement (*itnc2, *itnc1, combination)) {
               // Replace constraint by combination of both and remove