diff --git a/include/boost/program_options/variables_map.hpp b/include/boost/program_options/variables_map.hpp
index 362dedf283..7b91a7d4d8 100644
--- a/include/boost/program_options/variables_map.hpp
+++ b/include/boost/program_options/variables_map.hpp
@@ -50,7 +50,7 @@ namespace boost { namespace program_options {
 
 
     /** Runs all 'notify' function for options in 'm'. */
-    BOOST_PROGRAM_OPTIONS_DECL void notify(variables_map& m);
+    BOOST_PROGRAM_OPTIONS_DECL void notify(const variables_map& m);
 
     /** Class holding value of option. Contains details about how the
         value is set and allows to conveniently obtain the value.
@@ -157,7 +157,7 @@ namespace boost { namespace program_options {
         // Override to clear some extra fields.
         void clear();
 
-        void notify();
+        void notify() const;
 
     private:
         /** Implementation of abstract_variables_map::get
diff --git a/src/variables_map.cpp b/src/variables_map.cpp
index bc85f7e34b..2964ec29c2 100644
--- a/src/variables_map.cpp
+++ b/src/variables_map.cpp
@@ -148,7 +148,7 @@ namespace boost { namespace program_options {
     }
 
     BOOST_PROGRAM_OPTIONS_DECL
-    void notify(variables_map& vm)
+    void notify(const variables_map& vm)
     {
         vm.notify();
     }
@@ -210,7 +210,7 @@ namespace boost { namespace program_options {
     }
 
     void
-    variables_map::notify()
+    variables_map::notify() const
     {
         // This checks if all required options occur
         for (map<string, string>::const_iterator r = m_required.begin();
@@ -223,12 +223,11 @@ namespace boost { namespace program_options {
             if (iter == end() || iter->second.empty())
             {
                 boost::throw_exception(required_option(display_opt));
-
             }
         }
 
         // Lastly, run notify actions.
-        for (map<string, variable_value>::iterator k = begin();
+        for (map<string, variable_value>::const_iterator k = begin();
              k != end();
              ++k)
         {