diff --git a/dlib/optimization/optimization_stop_strategies.h b/dlib/optimization/optimization_stop_strategies.h
index 139b552d5..a0243cacf 100644
--- a/dlib/optimization/optimization_stop_strategies.h
+++ b/dlib/optimization/optimization_stop_strategies.h
@@ -44,8 +44,8 @@ namespace dlib
             );
         }
 
-        const objective_delta_stop_strategy& be_verbose( 
-        ) const
+        objective_delta_stop_strategy& be_verbose( 
+        ) 
         {
             _verbose = true;
             return *this;
@@ -83,7 +83,7 @@ namespace dlib
         }
 
     private:
-        mutable bool _verbose;
+        bool _verbose;
 
         bool _been_used;
         double _min_delta;
@@ -123,8 +123,8 @@ namespace dlib
             );
         }
 
-        const gradient_norm_stop_strategy& be_verbose( 
-        ) const
+        gradient_norm_stop_strategy& be_verbose( 
+        ) 
         {
             _verbose = true;
             return *this;
@@ -158,7 +158,7 @@ namespace dlib
         }
 
     private:
-        mutable bool _verbose;
+        bool _verbose;
 
         double _min_norm;
         unsigned long _max_iter;
diff --git a/dlib/optimization/optimization_stop_strategies_abstract.h b/dlib/optimization/optimization_stop_strategies_abstract.h
index c5f5c7526..6a999f8d9 100644
--- a/dlib/optimization/optimization_stop_strategies_abstract.h
+++ b/dlib/optimization/optimization_stop_strategies_abstract.h
@@ -53,8 +53,8 @@ namespace dlib
                   executed.
         !*/
 
-        const objective_delta_stop_strategy& be_verbose( 
-        ) const;
+        objective_delta_stop_strategy& be_verbose( 
+        );
         /*!
             ensures
                 - causes this object to print status messages to standard out 
@@ -120,8 +120,8 @@ namespace dlib
                   max_iter iterations has been executed.
         !*/
 
-        const gradient_norm_stop_strategy& be_verbose( 
-        ) const;
+        gradient_norm_stop_strategy& be_verbose( 
+        );
         /*!
             ensures
                 - causes this object to print status messages to standard out