diff --git a/sql/field.cc b/sql/field.cc
index ba0ebb253f4..846bb1fe674 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -10598,7 +10598,7 @@ Column_definition::Column_definition(THD *thd, Field *old_field,
     length
 */
 
-uint32 Field_blob::char_length()
+uint32 Field_blob::char_length() const
 {
   switch (packlength)
   {
diff --git a/sql/field.h b/sql/field.h
index f550dad1c6c..0bb9da83827 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -1335,7 +1335,7 @@ public:
   longlong convert_decimal2longlong(const my_decimal *val, bool unsigned_flag,
                                     int *err);
   /* The max. number of characters */
-  virtual uint32 char_length()
+  virtual uint32 char_length() const
   {
     return field_length / charset()->mbmaxlen;
   }
@@ -3316,7 +3316,7 @@ public:
   bool has_charset(void) const
   { return charset() == &my_charset_bin ? FALSE : TRUE; }
   uint32 max_display_length();
-  uint32 char_length();
+  uint32 char_length() const;
   uint is_equal(Create_field *new_field);
 private:
   int do_save_field_metadata(uchar *first_byte);