diff --git a/sql/item_sum.cc b/sql/item_sum.cc
index 68aa52f561c..f72b64fc66e 100644
--- a/sql/item_sum.cc
+++ b/sql/item_sum.cc
@@ -28,6 +28,18 @@
 #include "mysql_priv.h"
 #include "sql_select.h"
 
+/**
+  Calculate the affordable RAM limit for structures like TREE or Unique
+  used in Item_sum_*
+*/
+
+ulonglong Item_sum::ram_limitation(THD *thd)
+{
+  return min(thd->variables.tmp_table_size,
+      thd->variables.max_heap_table_size);
+}
+
+
 /**
   Prepare an aggregate function item for checking context conditions.
 
@@ -833,7 +845,7 @@ bool Aggregator_distinct::setup(THD *thd)
       }
       DBUG_ASSERT(tree == 0);
       tree= new Unique(compare_key, cmp_arg, tree_key_length,
-                       thd->variables.max_heap_table_size);
+                       item_sum->ram_limitation(thd));
       /*
         The only time tree_key_length could be 0 is if someone does
         count(distinct) on a char(0) field - stupid thing to do,
@@ -902,7 +914,7 @@ bool Aggregator_distinct::setup(THD *thd)
       are converted to binary representation as well.
     */
     tree= new Unique(simple_raw_key_cmp, &tree_key_length, tree_key_length,
-                       thd->variables.max_heap_table_size);
+                     item_sum->ram_limitation(thd));
 
     DBUG_RETURN(tree == 0);
   }
@@ -3514,7 +3526,7 @@ bool Item_func_group_concat::setup(THD *thd)
     unique_filter= new Unique(group_concat_key_cmp_with_distinct,
                               (void*)this,
                               tree_key_length,
-                              thd->variables.max_heap_table_size);
+                              ram_limitation(thd));
   
   DBUG_RETURN(FALSE);
 }
diff --git a/sql/item_sum.h b/sql/item_sum.h
index 6d7418204fc..9e062ce1d16 100644
--- a/sql/item_sum.h
+++ b/sql/item_sum.h
@@ -364,6 +364,7 @@ protected:
   Item **orig_args, *tmp_orig_args[2];
   table_map used_tables_cache;
   bool forced_const;
+  static ulonglong ram_limitation(THD *thd);
 
 public: