diff -r 71fd280363d5 -r 4efe7b32b134 lemon/bits/edge_set_extender.h
--- a/lemon/bits/edge_set_extender.h	Tue Dec 20 17:38:19 2011 +0100
+++ b/lemon/bits/edge_set_extender.h	Tue Dec 20 17:43:11 2011 +0100
@@ -539,7 +539,7 @@
       typedef MapExtender<DefaultMap<Graph, Arc, _Value> > Parent;
 
     public:
-      ArcMap(const Graph& _g) 
+      explicit ArcMap(const Graph& _g) 
 	: Parent(_g) {}
       ArcMap(const Graph& _g, const _Value& _v) 
 	: Parent(_g, _v) {}
@@ -563,7 +563,7 @@
       typedef MapExtender<DefaultMap<Graph, Edge, _Value> > Parent;
 
     public:
-      EdgeMap(const Graph& _g) 
+      explicit EdgeMap(const Graph& _g) 
 	: Parent(_g) {}
 
       EdgeMap(const Graph& _g, const _Value& _v)