diff --git a/src/LR0.cpp b/src/LR0.cpp
index db1a73d9..a1a77174 100644
--- a/src/LR0.cpp
+++ b/src/LR0.cpp
@@ -158,7 +158,7 @@ std::string LR0::dump (std::vector <std::vector <std::string>>& augmented, State
 */
 
 ////////////////////////////////////////////////////////////////////////////////
-LR0::Item::Item (std::vector <std::string>& rule)
+LR0::Item::Item (const std::vector <std::string>& rule)
 : _rule (rule)
 , _cursor (2)
 {
diff --git a/src/LR0.h b/src/LR0.h
index 46224bbd..1172bdcd 100644
--- a/src/LR0.h
+++ b/src/LR0.h
@@ -40,11 +40,10 @@ public:
   void debug (bool);
   std::string dump () const;
 
-protected:
   class Item
   {
   public:
-    Item (std::vector <std::string>&);
+    Item (const std::vector <std::string>&);
     bool advance ();
 
   private: