diff --git a/mysql-test/r/lock_sync.result b/mysql-test/r/lock_sync.result
index 0b57b38f5ec..4eddbd170d9 100644
--- a/mysql-test/r/lock_sync.result
+++ b/mysql-test/r/lock_sync.result
@@ -60,6 +60,8 @@ release_lock("lock_bug45143_wait")
 1
 # Switch to connection 'con_bug45143_1'.
 # Reap INSERT statement.
+Warnings:
+Note	1592	Statement may not be safe to log in statement format.
 # Switch to connection 'con_bug45143_3'.
 # Reap LOCK TABLES statement.
 unlock tables;
@@ -69,3 +71,23 @@ set debug_sync= 'RESET';
 set @@global.general_log= @old_general_log;
 drop view v1;
 drop table t1;
+#
+# Bug#50821 Deadlock between LOCK TABLES and ALTER TABLE
+#
+DROP TABLE IF EXISTS t1, t2;
+CREATE TABLE t1(id INT);
+CREATE TABLE t2(id INT);
+# Connection con2
+START TRANSACTION;
+SELECT * FROM t1;
+id
+# Connection default
+# Sending:
+ALTER TABLE t1 ADD COLUMN j INT;
+# Connection con2
+# This used to cause a deadlock.
+INSERT INTO t2 SELECT * FROM t1;
+COMMIT;
+# Connection default
+# Reaping ALTER TABLE t1 ADD COLUMN j INT
+DROP TABLE t1, t2;
diff --git a/mysql-test/t/lock_sync.test b/mysql-test/t/lock_sync.test
index 460c0175808..6974a8ec968 100644
--- a/mysql-test/t/lock_sync.test
+++ b/mysql-test/t/lock_sync.test
@@ -4,6 +4,10 @@
 --source include/have_debug_sync.inc
 # We need InnoDB to be able use TL_WRITE_ALLOW_WRITE type of locks in our tests.
 --source include/have_innodb.inc
+# The test for Bug#50821 requires binary logging turned on.
+# With binary logging on, sub-queries in DML statements acquire
+# TL_READ_NO_INSERT which was needed to reproduce this deadlock bug.
+--source include/have_log_bin.inc
 # Until bug#41971 'Thread state on embedded server is always "Writing to net"'
 # is fixed this test can't be run on embedded version of server.
 --source include/not_embedded.inc
@@ -118,6 +122,49 @@ drop view v1;
 drop table t1;
 
 
+--echo #
+--echo # Bug#50821 Deadlock between LOCK TABLES and ALTER TABLE
+--echo #
+
+--disable_warnings
+DROP TABLE IF EXISTS t1, t2;
+--enable_warnings
+
+CREATE TABLE t1(id INT);
+CREATE TABLE t2(id INT);
+
+--echo # Connection con2
+connect (con2, localhost, root);
+START TRANSACTION;
+SELECT * FROM t1;
+
+--echo # Connection default
+connection default;
+--echo # Sending:
+--send ALTER TABLE t1 ADD COLUMN j INT
+
+--echo # Connection con2
+connection con2;
+let $wait_condition=
+  SELECT COUNT(*) = 1 FROM information_schema.processlist
+  WHERE state = "Waiting for table" 
+  AND info = "ALTER TABLE t1 ADD COLUMN j INT";
+--source include/wait_condition.inc
+
+--echo # This used to cause a deadlock.
+INSERT INTO t2 SELECT * FROM t1;
+
+COMMIT;
+
+--echo # Connection default
+connection default;
+--echo # Reaping ALTER TABLE t1 ADD COLUMN j INT
+--reap
+
+DROP TABLE t1, t2;
+disconnect con2;
+
+
 # Check that all connections opened by test cases in this file are really
 # gone so execution of other tests won't be affected by their presence.
 --source include/wait_until_count_sessions.inc
diff --git a/mysys/thr_lock.c b/mysys/thr_lock.c
index 6d62476ecf3..901620d3a93 100644
--- a/mysys/thr_lock.c
+++ b/mysys/thr_lock.c
@@ -549,7 +549,7 @@ thr_lock(THR_LOCK_DATA *data, THR_LOCK_OWNER *owner,
            Request
           /-------
          H|++++  WRITE_ALLOW_WRITE
-         e|+++-  WRITE_ALLOW_READ
+         e|++++  WRITE_ALLOW_READ
          l|+++-  WRITE_CONCURRENT_INSERT
          d|++++  WRITE_DELAYED
            ||||
@@ -572,8 +572,7 @@ thr_lock(THR_LOCK_DATA *data, THR_LOCK_OWNER *owner,
       if (thr_lock_owner_equal(data->owner, lock->write.data->owner) ||
 	  (lock->write.data->type <= TL_WRITE_DELAYED &&
 	   (((int) lock_type <= (int) TL_READ_HIGH_PRIORITY) ||
-	    (lock->write.data->type != TL_WRITE_CONCURRENT_INSERT &&
-	     lock->write.data->type != TL_WRITE_ALLOW_READ))))
+	    (lock->write.data->type != TL_WRITE_CONCURRENT_INSERT))))
       {						/* Already got a write lock */
 	(*lock->read.last)=data;		/* Add to running FIFO */
 	data->prev=lock->read.last;