diff --git a/src/libutil/aterm-map.hh b/src/libutil/aterm-map.hh
index 078617a7d6..203b42934a 100644
--- a/src/libutil/aterm-map.hh
+++ b/src/libutil/aterm-map.hh
@@ -89,6 +89,8 @@ public:
         }
     };
 
+    friend class ATermMap::const_iterator;
+    
     const_iterator begin() const
     {
         unsigned int i = 0;