--- a/liboctave/cmd-hist.h
+++ b/liboctave/cmd-hist.h
@@ -146,31 +146,31 @@
 
   virtual void do_set_size (int);
 
-  virtual int do_size (void);
+  virtual int do_size (void) const;
 
   virtual void do_ignore_entries (bool);
 
-  virtual bool do_ignoring_entries (void);
+  virtual bool do_ignoring_entries (void) const;
 
   virtual void do_add (const std::string&);
 
   virtual void do_remove (int);
 
-  virtual int do_where (void);
+  virtual int do_where (void) const;
 
-  virtual int do_length (void);
+  virtual int do_length (void) const;
 
-  virtual int do_max_input_history (void);
+  virtual int do_max_input_history (void) const;
 
-  virtual int do_base (void);
+  virtual int do_base (void) const;
 
-  virtual int do_current_number (void);
+  virtual int do_current_number (void) const;
 
   virtual void do_stifle (int);
 
   virtual int do_unstifle (void);
 
-  virtual int do_is_stifled (void);
+  virtual int do_is_stifled (void) const;
 
   virtual void do_set_mark (int);
 
@@ -180,23 +180,23 @@
 
   virtual void do_read_range (const std::string&, int, int, bool);
 
-  virtual void do_write (const std::string&);
+  virtual void do_write (const std::string&) const;
 
   virtual void do_append (const std::string&);
 
-  virtual void do_truncate_file (const std::string&, int);
+  virtual void do_truncate_file (const std::string&, int) const;
 
-  virtual string_vector do_list (int, bool);
+  virtual string_vector do_list (int, bool) const;
 
-  virtual std::string do_get_entry (int);
+  virtual std::string do_get_entry (int) const;
 
   virtual void do_replace_entry (int, const std::string&);
 
   virtual void do_clean_up_and_save (const std::string&, int);
 
-  void error (int);
+  void error (int) const;
 
-  void error (const std::string&);
+  void error (const std::string&) const;
 
   // TRUE means we have initialized the history file name and number of
   // lines to save.