diff --git a/lemon/adaptors.h b/lemon/adaptors.h
--- a/lemon/adaptors.h
+++ b/lemon/adaptors.h
@@ -30,6 +30,7 @@
 #include <lemon/bits/variant.h>
 
 #include <lemon/bits/graph_adaptor_extender.h>
+#include <lemon/bits/map_extender.h>
 #include <lemon/tolerance.h>
 
 #include <algorithm>