diff --git a/mysql-test/suite/rpl/r/rpl_parallel2.result b/mysql-test/suite/rpl/r/rpl_parallel2.result
new file mode 100644
index 00000000000..49be484f419
--- /dev/null
+++ b/mysql-test/suite/rpl/r/rpl_parallel2.result
@@ -0,0 +1,18 @@
+include/rpl_init.inc [topology=1->2]
+*** MDEV-5509: Incorrect value for Seconds_Behind_Master if parallel replication ***
+SET @old_parallel_threads=@@GLOBAL.slave_parallel_threads;
+include/stop_slave.inc
+SET GLOBAL slave_parallel_threads=5;
+include/start_slave.inc
+CREATE TABLE t1 (a INT PRIMARY KEY, b INT);
+CALL mtr.add_suppression("Unsafe statement written to the binary log using statement format since BINLOG_FORMAT = STATEMENT. Statement is unsafe because it uses a system function that may return a different value on the slave");
+INSERT INTO t1 VALUES (1,sleep(2));
+Warnings:
+Note	1592	Unsafe statement written to the binary log using statement format since BINLOG_FORMAT = STATEMENT. Statement is unsafe because it uses a system function that may return a different value on the slave.
+Seconds_Behind_Master should be zero here because the slave is fully caught up and idle.
+Seconds_Behind_Master = '0'
+include/stop_slave.inc
+SET GLOBAL slave_parallel_threads=@old_parallel_threads;
+include/start_slave.inc
+DROP TABLE t1;
+include/rpl_end.inc
diff --git a/mysql-test/suite/rpl/t/rpl_parallel2.test b/mysql-test/suite/rpl/t/rpl_parallel2.test
new file mode 100644
index 00000000000..39b35063c7c
--- /dev/null
+++ b/mysql-test/suite/rpl/t/rpl_parallel2.test
@@ -0,0 +1,41 @@
+--source include/have_binlog_format_statement.inc
+--let $rpl_topology=1->2
+--source include/rpl_init.inc
+
+--echo *** MDEV-5509: Incorrect value for Seconds_Behind_Master if parallel replication ***
+
+--connection server_2
+SET @old_parallel_threads=@@GLOBAL.slave_parallel_threads;
+--source include/stop_slave.inc
+SET GLOBAL slave_parallel_threads=5;
+--source include/start_slave.inc
+
+--connection server_1
+CREATE TABLE t1 (a INT PRIMARY KEY, b INT);
+CALL mtr.add_suppression("Unsafe statement written to the binary log using statement format since BINLOG_FORMAT = STATEMENT. Statement is unsafe because it uses a system function that may return a different value on the slave");
+--save_master_pos
+
+--connection server_2
+--sync_with_master
+
+--connection server_1
+INSERT INTO t1 VALUES (1,sleep(2));
+--save_master_pos
+
+--connection server_2
+--sync_with_master
+
+--echo Seconds_Behind_Master should be zero here because the slave is fully caught up and idle.
+--let $status_items= Seconds_Behind_Master
+--source include/show_slave_status.inc
+
+
+--connection server_2
+--source include/stop_slave.inc
+SET GLOBAL slave_parallel_threads=@old_parallel_threads;
+--source include/start_slave.inc
+
+--connection server_1
+DROP TABLE t1;
+
+--source include/rpl_end.inc
diff --git a/sql/rpl_parallel.cc b/sql/rpl_parallel.cc
index af44d79038c..ef282611f70 100644
--- a/sql/rpl_parallel.cc
+++ b/sql/rpl_parallel.cc
@@ -766,6 +766,27 @@ rpl_parallel::wait_for_done()
 }
 
 
+bool
+rpl_parallel::workers_idle()
+{
+  struct rpl_parallel_entry *e;
+  uint32 i, max_i;
+
+  max_i= domain_hash.records;
+  for (i= 0; i < max_i; ++i)
+  {
+    bool active;
+    e= (struct rpl_parallel_entry *)my_hash_element(&domain_hash, i);
+    mysql_mutex_lock(&e->LOCK_parallel_entry);
+    active= e->current_sub_id > e->last_committed_sub_id;
+    mysql_mutex_unlock(&e->LOCK_parallel_entry);
+    if (active)
+      break;
+  }
+  return (i == max_i);
+}
+
+
 /*
   do_event() is executed by the sql_driver_thd thread.
   It's main purpose is to find a thread that can execute the query.
diff --git a/sql/rpl_parallel.h b/sql/rpl_parallel.h
index 0e88e09652b..019a354c57d 100644
--- a/sql/rpl_parallel.h
+++ b/sql/rpl_parallel.h
@@ -117,6 +117,7 @@ struct rpl_parallel {
   void reset();
   rpl_parallel_entry *find(uint32 domain_id);
   void wait_for_done();
+  bool workers_idle();
   bool do_event(rpl_group_info *serial_rgi, Log_event *ev,
                 ulonglong event_size);
 };
diff --git a/sql/rpl_rli.cc b/sql/rpl_rli.cc
index cfa7c0f344f..7f0ec702b87 100644
--- a/sql/rpl_rli.cc
+++ b/sql/rpl_rli.cc
@@ -56,7 +56,7 @@ Relay_log_info::Relay_log_info(bool is_slave_recovery)
    is_fake(FALSE),
 #endif
    group_master_log_pos(0), log_space_total(0), ignore_log_space_limit(0),
-   last_master_timestamp(0), slave_skip_counter(0),
+   last_master_timestamp(0), sql_thread_caught_up(true), slave_skip_counter(0),
    abort_pos_wait(0), slave_run_id(0), sql_driver_thd(),
    inited(0), abort_slave(0), slave_running(0), until_condition(UNTIL_NONE),
    until_log_pos(0), retried_trans(0), executed_entries(0),
@@ -1287,9 +1287,14 @@ void Relay_log_info::stmt_done(my_off_t event_master_log_pos,
       (probably ok - except in some very rare cases, only consequence
       is that value may take some time to display in
       Seconds_Behind_Master - not critical).
+
+      In parallel replication, we take care to not set last_master_timestamp
+      backwards, in case of out-of-order calls here.
     */
     if (!(event_creation_time == 0 &&
-          IF_DBUG(debug_not_change_ts_if_art_event > 0, 1)))
+          IF_DBUG(debug_not_change_ts_if_art_event > 0, 1)) &&
+        !(rgi->is_parallel_exec && event_creation_time <= last_master_timestamp)
+        )
         last_master_timestamp= event_creation_time;
   }
   DBUG_VOID_RETURN;
diff --git a/sql/rpl_rli.h b/sql/rpl_rli.h
index ff2ffd0b366..6716718d354 100644
--- a/sql/rpl_rli.h
+++ b/sql/rpl_rli.h
@@ -221,6 +221,12 @@ public:
   bool sql_force_rotate_relay;
 
   time_t last_master_timestamp;
+  /*
+    The SQL driver thread sets this true while it is waiting at the end of the
+    relay log for more events to arrive. SHOW SLAVE STATUS uses this to report
+    Seconds_Behind_Master as zero while the SQL thread is so waiting.
+  */
+  bool sql_thread_caught_up;
 
   void clear_until_condition();
 
diff --git a/sql/slave.cc b/sql/slave.cc
index a887ad9d924..07209c30ff3 100644
--- a/sql/slave.cc
+++ b/sql/slave.cc
@@ -2619,8 +2619,24 @@ static bool send_show_master_info_data(THD *thd, Master_info *mi, bool full,
     if ((mi->slave_running == MYSQL_SLAVE_RUN_CONNECT) &&
         mi->rli.slave_running)
     {
-      long time_diff= ((long)(time(0) - mi->rli.last_master_timestamp)
-                       - mi->clock_diff_with_master);
+      long time_diff;
+      bool idle;
+      time_t stamp= mi->rli.last_master_timestamp;
+
+      if (!stamp)
+        idle= true;
+      else
+      {
+        idle= mi->rli.sql_thread_caught_up;
+        if (opt_slave_parallel_threads > 0 && idle &&
+            !mi->rli.parallel.workers_idle())
+          idle= false;
+      }
+      if (idle)
+        time_diff= 0;
+      else
+      {
+        time_diff= ((long)(time(0) - stamp) - mi->clock_diff_with_master);
       /*
         Apparently on some systems time_diff can be <0. Here are possible
         reasons related to MySQL:
@@ -2636,13 +2652,15 @@ static bool send_show_master_info_data(THD *thd, Master_info *mi, bool full,
         slave is 2. At SHOW SLAVE STATUS time, assume that the difference
         between timestamp of slave and rli->last_master_timestamp is 0
         (i.e. they are in the same second), then we get 0-(2-1)=-1 as a result.
-        This confuses users, so we don't go below 0: hence the max().
+        This confuses users, so we don't go below 0.
 
         last_master_timestamp == 0 (an "impossible" timestamp 1970) is a
         special marker to say "consider we have caught up".
       */
-      protocol->store((longlong)(mi->rli.last_master_timestamp ?
-                                 max(0, time_diff) : 0));
+        if (time_diff < 0)
+          time_diff= 0;
+      }
+      protocol->store((longlong)time_diff);
     }
     else
     {
@@ -6100,6 +6118,7 @@ static Log_event* next_event(rpl_group_info *rgi, ulonglong *event_size)
 
       if (hot_log)
         mysql_mutex_unlock(log_lock);
+      rli->sql_thread_caught_up= false;
       DBUG_RETURN(ev);
     }
     if (opt_reckless_slave)                     // For mysql-test
@@ -6137,12 +6156,10 @@ static Log_event* next_event(rpl_group_info *rgi, ulonglong *event_size)
           Seconds_Behind_Master would be zero only when master has no
           more updates in binlog for slave. The heartbeat can be sent
           in a (small) fraction of slave_net_timeout. Until it's done
-          rli->last_master_timestamp is temporarely (for time of
-          waiting for the following event) reset whenever EOF is
-          reached.
+          rli->sql_thread_caught_up is temporarely (for time of waiting for
+          the following event) set whenever EOF is reached.
         */
-        time_t save_timestamp= rli->last_master_timestamp;
-        rli->last_master_timestamp= 0;
+        rli->sql_thread_caught_up= true;
 
         DBUG_ASSERT(rli->relay_log.get_open_count() ==
                     rli->cur_log_old_open_count);
@@ -6268,7 +6285,7 @@ static Log_event* next_event(rpl_group_info *rgi, ulonglong *event_size)
         rli->relay_log.wait_for_update_relay_log(rli->sql_driver_thd);
         // re-acquire data lock since we released it earlier
         mysql_mutex_lock(&rli->data_lock);
-        rli->last_master_timestamp= save_timestamp;
+        rli->sql_thread_caught_up= false;
         continue;
       }
       /*