diff --git a/mysql-test/r/olap.result b/mysql-test/r/olap.result
index 7cdd5e1b152..a392de613f8 100644
--- a/mysql-test/r/olap.result
+++ b/mysql-test/r/olap.result
@@ -592,6 +592,21 @@ a	max(b)
 NULL	2
 a	1
 drop table t1;
+create table t1 (a varchar(22) not null , b int);
+insert into t1 values ("2006-07-01 21:30", 1), ("2006-07-01 23:30", 10);
+select left(a,10), a, sum(b) from t1 group by 1,2 with rollup;
+left(a,10)	a	sum(b)
+2006-07-01	2006-07-01 21:30	1
+2006-07-01	2006-07-01 23:30	10
+2006-07-01	NULL	11
+NULL	NULL	11
+select left(a,10) x, a, sum(b) from t1 group by x,a with rollup;
+x	a	sum(b)
+2006-07-01	2006-07-01 21:30	1
+2006-07-01	2006-07-01 23:30	10
+2006-07-01	NULL	11
+NULL	NULL	11
+drop table t1;
 CREATE TABLE t1(id int, type char(1));
 INSERT INTO t1 VALUES
 (1,"A"),(2,"C"),(3,"A"),(4,"A"),(5,"B"),
diff --git a/mysql-test/t/olap.test b/mysql-test/t/olap.test
index e34ac6a865c..4e5e7b72fc8 100644
--- a/mysql-test/t/olap.test
+++ b/mysql-test/t/olap.test
@@ -283,6 +283,15 @@ select a, max(b) from t1 group by a with rollup;
 select distinct a, max(b) from t1 group by a with rollup;
 drop table t1;
 
+#
+# Bug #20825: rollup puts non-equal values together
+#
+create table t1 (a varchar(22) not null , b int);
+insert into t1 values ("2006-07-01 21:30", 1), ("2006-07-01 23:30", 10);
+select left(a,10), a, sum(b) from t1 group by 1,2 with rollup;
+select left(a,10) x, a, sum(b) from t1 group by x,a with rollup;
+drop table t1;
+
 # End of 4.1 tests
 
 #
@@ -318,4 +327,3 @@ SELECT * FROM v1;
 
 DROP VIEW v1;
 DROP TABLE t1;
-# End of 4.1 tests
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index cb1c393457e..f86e9a13d53 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -14156,12 +14156,17 @@ bool JOIN::rollup_init()
   while ((item= it++))
   {
     ORDER *group_tmp;
+    bool found_in_group= 0;
+
     for (group_tmp= group_list; group_tmp; group_tmp= group_tmp->next)
     {
       if (*group_tmp->item == item)
+      {
         item->maybe_null= 1;
+        found_in_group= 1;
+      }
     }
-    if (item->type() == Item::FUNC_ITEM)
+    if (item->type() == Item::FUNC_ITEM && !found_in_group)
     {
       bool changed= FALSE;
       if (change_group_ref(thd, (Item_func *) item, group_list, &changed))