diff -r 012cd0ca3254 -r 66d160810c0a lemon/bits/default_map.h
--- a/lemon/bits/default_map.h	Thu Apr 13 17:22:17 2006 +0000
+++ b/lemon/bits/default_map.h	Thu Apr 13 17:57:03 2006 +0000
@@ -159,7 +159,7 @@
     typedef typename Parent::Graph Graph;
     typedef typename Parent::Value Value;
 
-    DefaultMap(const Graph& graph) : Parent(graph) {}
+    explicit DefaultMap(const Graph& graph) : Parent(graph) {}
     DefaultMap(const Graph& graph, const Value& value) 
       : Parent(graph, value) {}