diff --git a/mysql-test/main/slowlog_integrity.result b/mysql-test/main/slowlog_integrity.result
new file mode 100644
index 00000000000..f65fbf49c03
--- /dev/null
+++ b/mysql-test/main/slowlog_integrity.result
@@ -0,0 +1,108 @@
+#
+# MDEV-20281 "[ERROR] Failed to write to mysql.slow_log:" without
+# error reason
+#
+call mtr.add_suppression("Failed to write to mysql.slow_log:");
+SET @old_slow_query_log= @@global.slow_query_log;
+SET @old_log_output= @@global.log_output;
+SET @old_long_query_time= @@long_query_time;
+SET GLOBAL log_output= "TABLE";
+SET GLOBAL slow_query_log= ON;
+SET SESSION long_query_time= 0;
+select 1 from dual;
+1
+1
+show create table mysql.slow_log;
+Table	Create Table
+slow_log	CREATE TABLE `slow_log` (
+  `start_time` timestamp(6) NOT NULL DEFAULT current_timestamp(6) ON UPDATE current_timestamp(6),
+  `user_host` mediumtext NOT NULL,
+  `query_time` time(6) NOT NULL,
+  `lock_time` time(6) NOT NULL,
+  `rows_sent` bigint(20) unsigned NOT NULL,
+  `rows_examined` bigint(20) unsigned NOT NULL,
+  `db` varchar(512) NOT NULL,
+  `last_insert_id` int(11) NOT NULL,
+  `insert_id` int(11) NOT NULL,
+  `server_id` int(10) unsigned NOT NULL,
+  `sql_text` mediumtext NOT NULL,
+  `thread_id` bigint(21) unsigned NOT NULL,
+  `rows_affected` bigint(20) unsigned NOT NULL
+) ENGINE=CSV DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci COMMENT='Slow log'
+SET @@long_query_time= @old_long_query_time;
+SET @@global.log_output= "FILE";
+SET GLOBAL slow_query_log= OFF;
+drop table mysql.slow_log;
+# one field missing
+CREATE TABLE mysql.slow_log (
+`start_time` timestamp(6) NOT NULL DEFAULT current_timestamp(6) ON UPDATE current_timestamp(6),
+`user_host` mediumtext NOT NULL,
+`query_time` time(6) NOT NULL,
+`lock_time` time(6) NOT NULL,
+`rows_sent` bigint(20) unsigned NOT NULL,
+`rows_examined` bigint(20) unsigned NOT NULL,
+`db` varchar(512) NOT NULL,
+`last_insert_id` int(11) NOT NULL,
+`insert_id` int(11) NOT NULL,
+`server_id` int(10) unsigned NOT NULL,
+`sql_text` mediumtext NOT NULL,
+`thread_id` bigint(21) unsigned NOT NULL
+) ENGINE=CSV DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci COMMENT='Slow log';
+SET GLOBAL log_output= "TABLE";
+SET GLOBAL slow_query_log= ON;
+SET SESSION long_query_time= 0;
+select 1 from dual;
+1
+1
+SET @@long_query_time= @old_long_query_time;
+SET @@global.log_output= "FILE";
+SET GLOBAL slow_query_log= OFF;
+drop table mysql.slow_log;
+# crazy types
+CREATE TABLE mysql.slow_log (
+`start_time` timestamp(6) NOT NULL DEFAULT current_timestamp(6) ON UPDATE current_timestamp(6),
+`user_host` ENUM('apple','orange','pear') NOT NULL,
+`query_time` ENUM('apple','orange','pear') NOT NULL,
+`lock_time` ENUM('apple','orange','pear') NOT NULL,
+`rows_sent` ENUM('apple','orange','pear') NOT NULL,
+`rows_examined` ENUM('apple','orange','pear') NOT NULL,
+`db` ENUM('apple','orange','pear') NOT NULL,
+`last_insert_id` ENUM('apple','orange','pear') NOT NULL,
+`insert_id` ENUM('apple','orange','pear') NOT NULL,
+`server_id` ENUM('apple','orange','pear') NOT NULL,
+`sql_text` ENUM('apple','orange','pear') NOT NULL,
+`thread_id` ENUM('apple','orange','pear') NOT NULL,
+`rows_affected` ENUM('apple','orange','pear') NOT NULL
+) ENGINE=CSV DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci COMMENT='Slow log';
+SET GLOBAL log_output= "TABLE";
+SET GLOBAL slow_query_log= ON;
+SET SESSION long_query_time= 0;
+select 1 from dual;
+1
+1
+SET @@long_query_time= @old_long_query_time;
+SET @@global.log_output= "FILE";
+SET GLOBAL slow_query_log= OFF;
+drop table mysql.slow_log;
+# restore normal slow log table
+CREATE TABLE mysql.slow_log (
+`start_time` timestamp(6) NOT NULL DEFAULT current_timestamp(6) ON UPDATE current_timestamp(6),
+`user_host` mediumtext NOT NULL,
+`query_time` time(6) NOT NULL,
+`lock_time` time(6) NOT NULL,
+`rows_sent` bigint(20) unsigned NOT NULL,
+`rows_examined` bigint(20) unsigned NOT NULL,
+`db` varchar(512) NOT NULL,
+`last_insert_id` int(11) NOT NULL,
+`insert_id` int(11) NOT NULL,
+`server_id` int(10) unsigned NOT NULL,
+`sql_text` mediumtext NOT NULL,
+`thread_id` bigint(21) unsigned NOT NULL,
+`rows_affected` bigint(20) unsigned NOT NULL
+) ENGINE=CSV DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci COMMENT='Slow log';
+SET @@long_query_time= @old_long_query_time;
+SET @@global.log_output= @old_log_output;
+SET @@global.slow_query_log= @old_slow_query_log;
+FOUND 2 /incorrect number of fields in the log table/ in mysqld.1.err
+FOUND 2 /Can't write data \(possible incorrect log table structure\)/ in mysqld.1.err
+# End of 10.5 tests
diff --git a/mysql-test/main/slowlog_integrity.test b/mysql-test/main/slowlog_integrity.test
new file mode 100644
index 00000000000..8db3a5ee881
--- /dev/null
+++ b/mysql-test/main/slowlog_integrity.test
@@ -0,0 +1,113 @@
+source include/not_embedded.inc;
+
+--echo #
+--echo # MDEV-20281 "[ERROR] Failed to write to mysql.slow_log:" without
+--echo # error reason
+--echo #
+
+
+call mtr.add_suppression("Failed to write to mysql.slow_log:");
+
+--disable_ps_protocol
+SET @old_slow_query_log= @@global.slow_query_log;
+SET @old_log_output= @@global.log_output;
+SET @old_long_query_time= @@long_query_time;
+SET GLOBAL log_output= "TABLE";
+SET GLOBAL slow_query_log= ON;
+SET SESSION long_query_time= 0;
+
+select 1 from dual;
+
+show create table mysql.slow_log;
+
+SET @@long_query_time= @old_long_query_time;
+SET @@global.log_output= "FILE";
+SET GLOBAL slow_query_log= OFF;
+
+drop table mysql.slow_log;
+
+--echo # one field missing
+CREATE TABLE mysql.slow_log (
+  `start_time` timestamp(6) NOT NULL DEFAULT current_timestamp(6) ON UPDATE current_timestamp(6),
+  `user_host` mediumtext NOT NULL,
+  `query_time` time(6) NOT NULL,
+  `lock_time` time(6) NOT NULL,
+  `rows_sent` bigint(20) unsigned NOT NULL,
+  `rows_examined` bigint(20) unsigned NOT NULL,
+  `db` varchar(512) NOT NULL,
+  `last_insert_id` int(11) NOT NULL,
+  `insert_id` int(11) NOT NULL,
+  `server_id` int(10) unsigned NOT NULL,
+  `sql_text` mediumtext NOT NULL,
+  `thread_id` bigint(21) unsigned NOT NULL
+) ENGINE=CSV DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci COMMENT='Slow log';
+
+SET GLOBAL log_output= "TABLE";
+SET GLOBAL slow_query_log= ON;
+SET SESSION long_query_time= 0;
+
+select 1 from dual;
+
+SET @@long_query_time= @old_long_query_time;
+SET @@global.log_output= "FILE";
+SET GLOBAL slow_query_log= OFF;
+
+drop table mysql.slow_log;
+
+--echo # crazy types
+CREATE TABLE mysql.slow_log (
+  `start_time` timestamp(6) NOT NULL DEFAULT current_timestamp(6) ON UPDATE current_timestamp(6),
+  `user_host` ENUM('apple','orange','pear') NOT NULL,
+  `query_time` ENUM('apple','orange','pear') NOT NULL,
+  `lock_time` ENUM('apple','orange','pear') NOT NULL,
+  `rows_sent` ENUM('apple','orange','pear') NOT NULL,
+  `rows_examined` ENUM('apple','orange','pear') NOT NULL,
+  `db` ENUM('apple','orange','pear') NOT NULL,
+  `last_insert_id` ENUM('apple','orange','pear') NOT NULL,
+  `insert_id` ENUM('apple','orange','pear') NOT NULL,
+  `server_id` ENUM('apple','orange','pear') NOT NULL,
+  `sql_text` ENUM('apple','orange','pear') NOT NULL,
+  `thread_id` ENUM('apple','orange','pear') NOT NULL,
+  `rows_affected` ENUM('apple','orange','pear') NOT NULL
+) ENGINE=CSV DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci COMMENT='Slow log';
+
+SET GLOBAL log_output= "TABLE";
+SET GLOBAL slow_query_log= ON;
+SET SESSION long_query_time= 0;
+
+select 1 from dual;
+
+SET @@long_query_time= @old_long_query_time;
+SET @@global.log_output= "FILE";
+SET GLOBAL slow_query_log= OFF;
+
+drop table mysql.slow_log;
+
+--echo # restore normal slow log table
+CREATE TABLE mysql.slow_log (
+  `start_time` timestamp(6) NOT NULL DEFAULT current_timestamp(6) ON UPDATE current_timestamp(6),
+  `user_host` mediumtext NOT NULL,
+  `query_time` time(6) NOT NULL,
+  `lock_time` time(6) NOT NULL,
+  `rows_sent` bigint(20) unsigned NOT NULL,
+  `rows_examined` bigint(20) unsigned NOT NULL,
+  `db` varchar(512) NOT NULL,
+  `last_insert_id` int(11) NOT NULL,
+  `insert_id` int(11) NOT NULL,
+  `server_id` int(10) unsigned NOT NULL,
+  `sql_text` mediumtext NOT NULL,
+  `thread_id` bigint(21) unsigned NOT NULL,
+  `rows_affected` bigint(20) unsigned NOT NULL
+) ENGINE=CSV DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci COMMENT='Slow log';
+SET @@long_query_time= @old_long_query_time;
+SET @@global.log_output= @old_log_output;
+SET @@global.slow_query_log= @old_slow_query_log;
+--enable_ps_protocol
+
+--let SEARCH_FILE=$MYSQLTEST_VARDIR/log/mysqld.1.err
+--let SEARCH_PATTERN=incorrect number of fields in the log table
+--source include/search_pattern_in_file.inc
+--let SEARCH_PATTERN=Can't write data \(possible incorrect log table structure\)
+--source include/search_pattern_in_file.inc
+
+--echo # End of 10.5 tests
diff --git a/sql/log.cc b/sql/log.cc
index 32a1436f9a6..e459e3a5b52 100644
--- a/sql/log.cc
+++ b/sql/log.cc
@@ -694,6 +694,7 @@ bool Log_to_csv_event_handler::
 {
   TABLE_LIST table_list;
   TABLE *table;
+  const char *cause= 0;
   bool result= TRUE;
   bool need_close= FALSE;
   bool need_pop= FALSE;
@@ -728,13 +729,19 @@ bool Log_to_csv_event_handler::
   need_pop= TRUE;
 
   if (!(table= open_log_table(thd, &table_list, &open_tables_backup)))
+  {
+    cause= "can't open file";
     goto err;
+  }
 
   need_close= TRUE;
 
   if (table->file->extra(HA_EXTRA_MARK_AS_LOG_TABLE) ||
       table->file->ha_rnd_init_with_error(0))
+  {
+    cause= "can't initialize table handler";
     goto err;
+  }
 
   need_rnd_end= TRUE;
 
@@ -753,12 +760,20 @@ bool Log_to_csv_event_handler::
 
   /* check that all columns exist */
   if (table->s->fields < 6)
+  {
+    cause= "incorrect number of fields in the log table";
     goto err;
+  }
 
   DBUG_ASSERT(table->field[0]->type() == MYSQL_TYPE_TIMESTAMP);
 
-  table->field[0]->store_timestamp(
-                  hrtime_to_my_time(event_time), hrtime_sec_part(event_time));
+  if (table->field[0]->store_timestamp(hrtime_to_my_time(event_time),
+                                       hrtime_sec_part(event_time)))
+  {
+    cause= "Can't write data (possible incorrect log table structure)";
+    goto err;
+  }
+
 
   /* do a write */
   if (table->field[1]->store(user_host, user_host_len, client_cs) ||
@@ -766,7 +781,10 @@ bool Log_to_csv_event_handler::
       table->field[3]->store((longlong) global_system_variables.server_id,
                              TRUE) ||
       table->field[4]->store(command_type, command_type_len, client_cs))
+  {
+    cause= "Can't write data (possible incorrect log table structure)";
     goto err;
+  }
 
   /*
     A positive return value in store() means truncation.
@@ -774,7 +792,10 @@ bool Log_to_csv_event_handler::
   */
   table->field[5]->flags|= FIELDFLAG_HEX_ESCAPE;
   if (table->field[5]->store(sql_text, sql_text_len, client_cs) < 0)
+  {
+    cause= "Can't write data (possible incorrect log table structure)";
     goto err;
+  }
 
   /* mark all fields as not null */
   table->field[1]->set_notnull();
@@ -790,14 +811,22 @@ bool Log_to_csv_event_handler::
   }
 
   if (table->file->ha_write_row(table->record[0]))
+  {
+    cause= "Can't write record";
     goto err;
+  }
 
   result= FALSE;
 
 err:
   if (result && !thd->killed)
+  {
+    const char *msg= error_handler.message();
+    if (!msg || !msg[0])
+      msg= cause;
     sql_print_error("Failed to write to mysql.general_log: %s",
-                    error_handler.message());
+                    msg);
+  }
 
   if (need_rnd_end)
   {
@@ -850,6 +879,8 @@ bool Log_to_csv_event_handler::
 {
   TABLE_LIST table_list;
   TABLE *table;
+  const char *cause= 0;
+  const char *msg;
   bool result= TRUE;
   bool need_close= FALSE;
   bool need_rnd_end= FALSE;
@@ -874,13 +905,19 @@ bool Log_to_csv_event_handler::
                             TL_WRITE_CONCURRENT_INSERT);
 
   if (!(table= open_log_table(thd, &table_list, &open_tables_backup)))
+  {
+    cause= "can't open file";
     goto err;
+  }
 
   need_close= TRUE;
 
   if (table->file->extra(HA_EXTRA_MARK_AS_LOG_TABLE) ||
       table->file->ha_rnd_init_with_error(0))
+  {
+    cause= "can't initialize table handler";
     goto err;
+  }
 
   need_rnd_end= TRUE;
 
@@ -891,12 +928,19 @@ bool Log_to_csv_event_handler::
 
   /* check that all columns exist */
   if (table->s->fields < 13)
+  {
+    cause= "incorrect number of fields in the log table";
     goto err;
+  }
+
+  // It can be used in 13 places below so assign it here
+  cause= "Can't write data (possible incorrect log table structure)";
 
   /* store the time and user values */
   DBUG_ASSERT(table->field[0]->type() == MYSQL_TYPE_TIMESTAMP);
-  table->field[0]->store_timestamp(
-             hrtime_to_my_time(current_time), hrtime_sec_part(current_time));
+  if(table->field[0]->store_timestamp(hrtime_to_my_time(current_time),
+                                      hrtime_sec_part(current_time)))
+    goto err;
   if (table->field[1]->store(user_host, user_host_len, client_cs))
     goto err;
 
@@ -976,9 +1020,13 @@ bool Log_to_csv_event_handler::
                               (longlong) thd->get_stmt_da()->affected_rows() :
                               0, TRUE))
     goto err;
+  cause= 0; // just for safety
 
   if (table->file->ha_write_row(table->record[0]))
+  {
+    cause= "Can't write record";
     goto err;
+  }
 
   result= FALSE;
 
@@ -986,8 +1034,13 @@ err:
   thd->pop_internal_handler();
 
   if (result && !thd->killed)
+  {
+    msg= error_handler.message();
+    if (!msg || !msg[0])
+      msg= cause;
     sql_print_error("Failed to write to mysql.slow_log: %s",
-                    error_handler.message());
+                    msg);
+  }
 
   if (need_rnd_end)
   {