diff --git a/lemon/bits/graph_extender.h b/lemon/bits/graph_extender.h
--- a/lemon/bits/graph_extender.h
+++ b/lemon/bits/graph_extender.h
@@ -56,11 +56,11 @@
       return Parent::maxArcId();
     }
 
-    Node fromId(int id, Node) const {
+    static Node fromId(int id, Node) {
       return Parent::nodeFromId(id);
     }
 
-    Arc fromId(int id, Arc) const {
+    static Arc fromId(int id, Arc) {
       return Parent::arcFromId(id);
     }
 
@@ -355,15 +355,15 @@
       return Parent::maxEdgeId();
     }
 
-    Node fromId(int id, Node) const {
+    static Node fromId(int id, Node) {
       return Parent::nodeFromId(id);
     }
 
-    Arc fromId(int id, Arc) const {
+    static Arc fromId(int id, Arc) {
       return Parent::arcFromId(id);
     }
 
-    Edge fromId(int id, Edge) const {
+    static Edge fromId(int id, Edge) {
       return Parent::edgeFromId(id);
     }
 
@@ -604,7 +604,7 @@
       typedef MapExtender<DefaultMap<Graph, Node, _Value> > Parent;
 
     public:
-      NodeMap(const Graph& graph)
+      explicit NodeMap(const Graph& graph)
         : Parent(graph) {}
       NodeMap(const Graph& graph, const _Value& value)
         : Parent(graph, value) {}
@@ -628,7 +628,7 @@
       typedef MapExtender<DefaultMap<Graph, Arc, _Value> > Parent;
 
     public:
-      ArcMap(const Graph& graph)
+      explicit ArcMap(const Graph& graph)
         : Parent(graph) {}
       ArcMap(const Graph& graph, const _Value& value)
         : Parent(graph, value) {}
@@ -652,7 +652,7 @@
       typedef MapExtender<DefaultMap<Graph, Edge, _Value> > Parent;
 
     public:
-      EdgeMap(const Graph& graph)
+      explicit EdgeMap(const Graph& graph)
         : Parent(graph) {}
 
       EdgeMap(const Graph& graph, const _Value& value)