diff --git a/lemon/fractional_matching.h b/lemon/fractional_matching.h
--- a/lemon/fractional_matching.h
+++ b/lemon/fractional_matching.h
@@ -1166,6 +1166,11 @@
         (*_delta3_index)[e] = _delta3->PRE_HEAP;
       }
 
+      _delta1->clear();
+      _delta2->clear();
+      _delta3->clear();
+      _tree_set->clear();
+
       for (NodeIt n(_graph); n != INVALID; ++n) {
         Value max = 0;
         for (OutArcIt e(_graph, n); e != INVALID; ++e) {
@@ -1905,6 +1910,10 @@
         (*_delta3_index)[e] = _delta3->PRE_HEAP;
       }
 
+      _delta2->clear();
+      _delta3->clear();
+      _tree_set->clear();
+
       for (NodeIt n(_graph); n != INVALID; ++n) {
         Value max = - std::numeric_limits<Value>::max();
         for (OutArcIt e(_graph, n); e != INVALID; ++e) {