diff --git a/mysql-test/r/innodb_mysql.result b/mysql-test/r/innodb_mysql.result
index 402ab3c1b16..2d93cbb47b3 100644
--- a/mysql-test/r/innodb_mysql.result
+++ b/mysql-test/r/innodb_mysql.result
@@ -2273,4 +2273,35 @@ END|
 DROP PROCEDURE p1;
 DROP VIEW v1;
 DROP TABLE t1,t2;
+#
+# Bug #20837 Apparent change of isolation 
+#     level during transaction
+#
+SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;
+CREATE TABLE t1 (s1 INT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (1),(2);
+COMMIT;
+SET @@autocommit = 0;
+COMMIT;
+SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
+START TRANSACTION;
+SELECT * FROM t1;
+s1
+1
+2
+Should be READ UNCOMMITTED
+SELECT @@tx_isolation;
+@@tx_isolation
+READ-UNCOMMITTED
+INSERT INTO t1 VALUES (-1);
+Should be READ UNCOMMITTED
+SELECT @@tx_isolation;
+@@tx_isolation
+READ-UNCOMMITTED
+COMMIT;
+Should now be REPEATABLE READ
+SELECT @@tx_isolation;
+@@tx_isolation
+REPEATABLE-READ
+DROP TABLE t1;
 End of 5.1 tests
diff --git a/mysql-test/t/innodb_mysql.test b/mysql-test/t/innodb_mysql.test
index a2a1113598d..0462536371e 100644
--- a/mysql-test/t/innodb_mysql.test
+++ b/mysql-test/t/innodb_mysql.test
@@ -536,4 +536,30 @@ DROP PROCEDURE p1;
 DROP VIEW v1;
 DROP TABLE t1,t2;
 
+
+--echo #
+--echo # Bug #20837 Apparent change of isolation 
+--echo #     level during transaction
+--echo #
+
+SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;
+CREATE TABLE t1 (s1 INT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (1),(2);
+COMMIT;
+
+SET @@autocommit = 0;
+COMMIT;
+SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
+START TRANSACTION;
+SELECT * FROM t1;
+--echo Should be READ UNCOMMITTED
+SELECT @@tx_isolation;
+INSERT INTO t1 VALUES (-1);
+--echo Should be READ UNCOMMITTED
+SELECT @@tx_isolation;
+COMMIT;
+--echo Should now be REPEATABLE READ
+SELECT @@tx_isolation;
+DROP TABLE t1;
+
 --echo End of 5.1 tests
diff --git a/sql/handler.cc b/sql/handler.cc
index 216228ed509..f6cdaca05bd 100644
--- a/sql/handler.cc
+++ b/sql/handler.cc
@@ -1369,8 +1369,14 @@ int ha_autocommit_or_rollback(THD *thd, int error)
       if (thd->transaction_rollback_request && !thd->in_sub_stmt)
         (void) ha_rollback(thd);
     }
-
-    thd->variables.tx_isolation=thd->session_tx_isolation;
+  } 
+  else if (!(thd->options & (OPTION_NOT_AUTOCOMMIT | OPTION_BEGIN)))
+  {
+    /* 
+       If we're in autocommit mode, reset tx_isolation
+       to the default value
+    */
+    thd->variables.tx_isolation= thd->session_tx_isolation;
   }
 #endif
   DBUG_RETURN(error);