diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index 93e2edf9975..94370d45cef 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -2951,19 +2951,7 @@ String *Item_func_conv::val_str(String *str)
 String *Item_func_conv_charset::val_str(String *str)
 {
   DBUG_ASSERT(fixed == 1);
-  if (cached_value == CONST_WILL_BE_CACHED)
-  {
-    uint errors= 0;
-    String tmp, *str= args[0]->val_str(&tmp);
-    if (!str || str_value.copy(str->ptr(), str->length(),
-                               str->charset(), conv_charset, &errors))
-      null_value= 1;
-    cached_value= CACHED;
-    str_value.mark_as_const();
-    safe= (errors == 0);
-    is_expensive_cache= 0;
-  }
-  if (cached_value == CACHED)
+  if (use_cached_value)
     return null_value ? 0 : &str_value;
   String *arg= args[0]->val_str(str);
   uint dummy_errors;
diff --git a/sql/item_strfunc.h b/sql/item_strfunc.h
index 459dc5af34e..7606c281548 100644
--- a/sql/item_strfunc.h
+++ b/sql/item_strfunc.h
@@ -817,26 +817,31 @@ public:
 
 class Item_func_conv_charset :public Item_str_func
 {
+  bool use_cached_value;
   String tmp_value;
-  enum state_of_cache { NOT_CONST, CONST_WILL_BE_CACHED, CACHED };
-  enum state_of_cache cached_value;
 public:
   bool safe;
   CHARSET_INFO *conv_charset; // keep it public
-  Item_func_conv_charset(Item *a, CHARSET_INFO *cs) :Item_str_func(a),
-    cached_value(NOT_CONST), safe(0), conv_charset(cs)
-  {}
-  Item_func_conv_charset(Item *a, CHARSET_INFO *cs, bool cache_if_const)
-    :Item_str_func(a), conv_charset(cs)
+  Item_func_conv_charset(Item *a, CHARSET_INFO *cs) :Item_str_func(a) 
+  { conv_charset= cs; use_cached_value= 0; safe= 0; }
+  Item_func_conv_charset(Item *a, CHARSET_INFO *cs, bool cache_if_const) 
+    :Item_str_func(a) 
   {
-    if (cache_if_const && args[0]->const_item())
+    conv_charset= cs;
+    if (cache_if_const && args[0]->const_item() && !args[0]->is_expensive())
     {
-      is_expensive_cache= MY_TEST(args[0]->is_expensive());
-      cached_value= CONST_WILL_BE_CACHED;
+      uint errors= 0;
+      String tmp, *str= args[0]->val_str(&tmp);
+      if (!str || str_value.copy(str->ptr(), str->length(),
+                                 str->charset(), conv_charset, &errors))
+        null_value= 1;
+      use_cached_value= 1;
+      str_value.mark_as_const();
+      safe= (errors == 0);
     }
     else
     {
-      cached_value= NOT_CONST;
+      use_cached_value= 0;
       /*
         Conversion from and to "binary" is safe.
         Conversion to Unicode is safe.
@@ -887,7 +892,6 @@ public:
   void fix_length_and_dec();
   const char *func_name() const { return "convert"; }
   virtual void print(String *str, enum_query_type query_type);
-  virtual bool const_item() const { return cached_value != NOT_CONST; }
 };
 
 class Item_func_set_collation :public Item_str_func