diff --git a/mysql-test/r/order_by.result b/mysql-test/r/order_by.result
index f0e5b5fde3d..87b6c3f5455 100644
--- a/mysql-test/r/order_by.result
+++ b/mysql-test/r/order_by.result
@@ -1111,5 +1111,14 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c;
 col
 1
+# Must use ref-or-null on the a_c index
+EXPLAIN
+SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c DESC;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	ref_or_null	a_c,a	x	x	x	x	x
+# Must return 1 row
+SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c DESC;
+col
+1
 DROP TABLE t1;
 End of 5.0 tests
diff --git a/mysql-test/t/order_by.test b/mysql-test/t/order_by.test
index d9a6c0f844d..4da279cc8fd 100644
--- a/mysql-test/t/order_by.test
+++ b/mysql-test/t/order_by.test
@@ -778,6 +778,15 @@ SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c;
 --echo # Must return 1 row
 SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c;
 
+# part 2 of the problem : DESC test cases
+--echo # Must use ref-or-null on the a_c index
+--replace_column 1 x 2 x 3 x 6 x 7 x 8 x 9 x 10 x
+EXPLAIN
+SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c DESC;
+--echo # Must return 1 row
+SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c DESC;
+
+
 DROP TABLE t1;
 
 
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 9f0843fe0db..f655db0fc32 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -12824,7 +12824,7 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
 	  }
 	  DBUG_RETURN(1);
 	}
-	if (tab->ref.key_parts <= used_key_parts)
+	if (tab->ref.key_parts <= used_key_parts && tab->type == JT_REF)
 	{
 	  /*
 	    SELECT * FROM t1 WHERE a=1 ORDER BY a DESC,b DESC