diff --git a/mysql-test/r/join.result b/mysql-test/r/join.result
index 8691eb27220..102b39c3992 100644
--- a/mysql-test/r/join.result
+++ b/mysql-test/r/join.result
@@ -1145,3 +1145,14 @@ NULL
 NULL
 1
 DROP TABLE t1, t2, mm1;
+#
+# Bug #50335: Assertion `!(order->used & map)' in eq_ref_table
+# 
+CREATE TABLE t1 (a INT NOT NULL, b INT NOT NULL, PRIMARY KEY (a,b));
+INSERT INTO t1 VALUES (0,0), (1,1);
+SELECT * FROM t1 STRAIGHT_JOIN t1 t2 ON t1.a=t2.a AND t1.a=t2.b ORDER BY t2.a, t1.a;
+a	b	a	b
+0	0	0	0
+1	1	1	1
+DROP TABLE t1;
+End of 5.1 tests
diff --git a/mysql-test/t/join.test b/mysql-test/t/join.test
index 645321a3a5e..761121313e5 100644
--- a/mysql-test/t/join.test
+++ b/mysql-test/t/join.test
@@ -816,3 +816,16 @@ CREATE TABLE mm1(a CHAR(9),b INT,KEY(b),KEY(a))
 ENGINE=MERGE  UNION=(t1,t2);
 SELECT t1.a FROM mm1,t1;
 DROP TABLE t1, t2, mm1;
+
+--echo #
+--echo # Bug #50335: Assertion `!(order->used & map)' in eq_ref_table
+--echo # 
+
+CREATE TABLE t1 (a INT NOT NULL, b INT NOT NULL, PRIMARY KEY (a,b));
+INSERT INTO t1 VALUES (0,0), (1,1);
+
+SELECT * FROM t1 STRAIGHT_JOIN t1 t2 ON t1.a=t2.a AND t1.a=t2.b ORDER BY t2.a, t1.a;
+
+DROP TABLE t1;
+
+--echo End of 5.1 tests
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 52f9aae7a0c..b9f59fac4d6 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -7028,9 +7028,11 @@ eq_ref_table(JOIN *join, ORDER *start_order, JOIN_TAB *tab)
       }
       if (order)
       {
-	found++;
-	DBUG_ASSERT(!(order->used & map));
-	order->used|=map;
+        if (!(order->used & map))
+        {
+          found++;
+          order->used|= map;
+        }
 	continue;				// Used in ORDER BY
       }
       if (!only_eq_ref_tables(join,start_order, (*ref_item)->used_tables()))