diff --git a/mysql-test/main/backup_server_block.result b/mysql-test/main/backup_server_block.result
new file mode 100644
index 0000000000000..ce9b5582a68dd
--- /dev/null
+++ b/mysql-test/main/backup_server_block.result
@@ -0,0 +1,32 @@
+connect  con1,localhost,root,,test;
+connect  con2,localhost,root,,test;
+connection con1;
+SET DEBUG_SYNC='after_backup_server_lock_acquired SIGNAL in_progress WAIT_FOR finish';
+BACKUP SERVER TO '<MYSQLTEST_VARDIR>/some_directory';
+connection default;
+SET DEBUG_SYNC='now WAIT_FOR in_progress';
+connection con2;
+BACKUP SERVER TO '<MYSQLTEST_VARDIR>/other_directory';
+connection default;
+SET @con2_id = <con2_id>;
+SELECT COMMAND, STATE, INFO FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID = @con2_id;
+COMMAND	STATE	INFO
+Query	Waiting for backup lock	BACKUP SERVER TO '<MYSQLTEST_VARDIR>/other_directory'
+SET DEBUG_SYNC='now SIGNAL finish';
+connection con1;
+connection default;
+connection con2;
+connection default;
+SET DEBUG_SYNC='RESET';
+BACKUP STAGE START;
+connection con2;
+BACKUP SERVER TO '<MYSQLTEST_VARDIR>/another_directory';
+connection default;
+SELECT COMMAND, STATE, INFO FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID = @con2_id;
+COMMAND	STATE	INFO
+Query	Waiting for backup lock	BACKUP SERVER TO '<MYSQLTEST_VARDIR>/another_directory'
+BACKUP STAGE END;
+connection con2;
+connection default;
+disconnect con1;
+disconnect con2;
diff --git a/mysql-test/main/backup_server_block.test b/mysql-test/main/backup_server_block.test
new file mode 100644
index 0000000000000..8214367e0ea9e
--- /dev/null
+++ b/mysql-test/main/backup_server_block.test
@@ -0,0 +1,86 @@
+# Check that BACKUP SERVER blocks when another BACKUP SERVER is in progress
+
+--source include/have_debug_sync.inc
+
+--connect (con1,localhost,root,,test)
+--connect (con2,localhost,root,,test)
+
+--connection con1
+# Simulate long-running backup by blocking it on a debug sync point
+SET DEBUG_SYNC='after_backup_server_lock_acquired SIGNAL in_progress WAIT_FOR finish';
+--replace_result $MYSQLTEST_VARDIR <MYSQLTEST_VARDIR>
+--send_eval BACKUP SERVER TO '$MYSQLTEST_VARDIR/some_directory'
+
+--connection default
+# Wait for the "long-running" backup to lock the system
+SET DEBUG_SYNC='now WAIT_FOR in_progress';
+
+--connection con2
+let $con2_id= `SELECT CONNECTION_ID()`;
+# Attempt a backup while the other backup is running
+--replace_result $MYSQLTEST_VARDIR <MYSQLTEST_VARDIR>
+--send_eval BACKUP SERVER TO '$MYSQLTEST_VARDIR/other_directory'
+
+--connection default
+# Check that the backup on con2 is waiting for the backup on con1
+--replace_result $con2_id <con2_id>
+eval SET @con2_id = $con2_id;
+let $wait_condition=
+  SELECT COUNT(*) = 1 FROM INFORMATION_SCHEMA.PROCESSLIST
+  WHERE ID = @con2_id AND State = 'Waiting for backup lock';
+--source include/wait_condition.inc
+--replace_result $MYSQLTEST_VARDIR <MYSQLTEST_VARDIR>
+SELECT COMMAND, STATE, INFO FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID = @con2_id;
+
+SET DEBUG_SYNC='now SIGNAL finish';
+
+--connection con1
+--reap
+
+--connection default
+# When "long running" backup finishes, check that the backup on con2
+# is also allowed to finish
+let $wait_condition=
+  SELECT COUNT(*) = 0 FROM INFORMATION_SCHEMA.PROCESSLIST
+  WHERE Info LIKE 'BACKUP SERVER TO %' AND State = 'Waiting for backup lock';
+--source include/wait_condition.inc
+
+--connection con2
+--reap
+
+--connection default
+SET DEBUG_SYNC='RESET';
+
+# Test that BACKUP SERVER blocks when a BACKUP STAGE process is in progress
+
+BACKUP STAGE START;
+
+--connection con2
+--replace_result $MYSQLTEST_VARDIR <MYSQLTEST_VARDIR>
+--send_eval BACKUP SERVER TO '$MYSQLTEST_VARDIR/another_directory'
+
+--connection default
+let $wait_condition=
+  SELECT COUNT(*) = 1 FROM INFORMATION_SCHEMA.PROCESSLIST
+  WHERE ID = @con2_id AND State = 'Waiting for backup lock';
+--source include/wait_condition.inc
+--replace_result $MYSQLTEST_VARDIR <MYSQLTEST_VARDIR>
+SELECT COMMAND, STATE, INFO FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID = @con2_id;
+
+BACKUP STAGE END;
+
+# When "long running" backup finishes, check that the backup on con2
+# is also allowed to finish
+let $wait_condition=
+  SELECT COUNT(*) = 0 FROM INFORMATION_SCHEMA.PROCESSLIST
+  WHERE Info LIKE 'BACKUP SERVER TO %' AND State = 'Waiting for backup lock';
+--source include/wait_condition.inc
+
+--connection con2
+--reap
+
+--connection default
+
+--disconnect con1
+--disconnect con2
+
diff --git a/sql/debug_sync.h b/sql/debug_sync.h
index f0897aae2ff8d..c885056637dba 100644
--- a/sql/debug_sync.h
+++ b/sql/debug_sync.h
@@ -22,6 +22,8 @@
   Declarations for the Debug Sync Facility. See debug_sync.cc for details.
 */
 
+#include <my_global.h>
+
 class THD;
 
 #if defined(ENABLED_DEBUG_SYNC)
diff --git a/sql/mdl.h b/sql/mdl.h
index 1b01bcf3ecb7b..0c3159182cf4f 100644
--- a/sql/mdl.h
+++ b/sql/mdl.h
@@ -578,7 +578,7 @@ class MDL_request
   /** Set type of lock request. Can be only applied to pending locks. */
   inline void set_type(enum_mdl_type type_arg)
   {
-    DBUG_ASSERT(ticket == NULL);
+    DBUG_ASSERT(ticket == nullptr);
     type= type_arg;
   }
   void move_from(MDL_request &from)
@@ -589,7 +589,7 @@ class MDL_request
     next_in_list= from.next_in_list;
     prev_in_list= from.prev_in_list;
     key.mdl_key_init(&from.key);
-    from.ticket=  NULL; // that's what "move" means
+    from.ticket=  nullptr; // that's what "move" means
   }
 
   /**
@@ -621,17 +621,17 @@ class MDL_request
   MDL_request& operator=(const MDL_request &)
   {
     type= MDL_NOT_INITIALIZED;
-    ticket= NULL;
+    ticket= nullptr;
     /* Do nothing, in particular, don't try to copy the key. */
     return *this;
   }
   /* Another piece of ugliness for TABLE_LIST constructor */
-  MDL_request(): type(MDL_NOT_INITIALIZED), ticket(NULL) {}
+  MDL_request(): type(MDL_NOT_INITIALIZED), ticket(nullptr) {}
 
   MDL_request(const MDL_request *rhs)
     :type(rhs->type),
     duration(rhs->duration),
-    ticket(NULL),
+    ticket(nullptr),
     key(&rhs->key)
   {}
 };
@@ -1088,7 +1088,7 @@ class MDL_context
   void done_waiting_for()
   {
     mysql_prlock_wrlock(&m_LOCK_waiting_for);
-    m_waiting_for= NULL;
+    m_waiting_for= nullptr;
     mysql_prlock_unlock(&m_LOCK_waiting_for);
   }
   void lock_deadlock_victim()
@@ -1116,7 +1116,7 @@ class MDL_context
     The coordinator thread holds the lock for the duration of worker's purge
     job, or longer, possibly reusing shared MDL for different workers and jobs.
   */
-  MDL_context *lock_warrant= NULL;
+  MDL_context *lock_warrant= nullptr;
 
   inline bool is_lock_warrantee(MDL_key::enum_mdl_namespace ns,
                                 const char *db, const char *name,
diff --git a/sql/sql_plist.h b/sql/sql_plist.h
index 0969fef07491a..b9c8ba71247e8 100644
--- a/sql/sql_plist.h
+++ b/sql/sql_plist.h
@@ -16,6 +16,8 @@
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */
 
 
+#include <my_global.h>
+
 template <typename T, typename L>
 class I_P_List_iterator;
 class I_P_List_null_counter;
@@ -72,14 +74,14 @@ class I_P_List : public C, public I
     is a bad idea.
   */
 public:
-  I_P_List() : I(&m_first), m_first(NULL) {};
+  I_P_List() : I(&m_first), m_first(nullptr) {};
   /*
     empty() is used in many places in the code instead of a constructor, to
     initialize a bzero-ed I_P_List instance.
   */
 
-  inline void empty()      { m_first= NULL; C::reset(); I::set_last(&m_first); }
-  inline bool is_empty() const { return (m_first == NULL); }
+  inline void empty()      { m_first= nullptr; C::reset(); I::set_last(&m_first); }
+  inline bool is_empty() const { return (m_first == nullptr); }
   inline void push_front(T* a)
   {
     *B::next_ptr(a)= m_first;
@@ -102,7 +104,7 @@ class I_P_List : public C, public I
   }
   inline void insert_after(T *pos, T *a)
   {
-    if (pos == NULL)
+    if (pos == nullptr)
       push_front(a);
     else
     {