diff --git a/mysql-test/suite/maria/maria-recovery-corrupt-change.result b/mysql-test/suite/maria/maria-recovery-corrupt-change.result
new file mode 100644
index 0000000000000..2ce6e8e1baf12
--- /dev/null
+++ b/mysql-test/suite/maria/maria-recovery-corrupt-change.result
@@ -0,0 +1,38 @@
+call mtr.add_suppression("File '.*aria_log.000.*' not found");
+drop database if exists mysqltest;
+create database mysqltest;
+connect  admin, localhost, root,,mysqltest,,;
+connection default;
+use mysqltest;
+connection default;
+connection admin;
+* shut down mysqld, removed logs, restarted it
+connection default;
+create table t1 (a int, b varchar(60), key(a), key(b))
+transactional=1 row_format=page engine=aria;
+set session debug_dbug="+d,corrupt_change_length";
+select count(*) from t1;
+count(*)
+200
+set session debug_dbug="+d,maria_flush_whole_log,maria_crash";
+set global aria_checkpoint_interval=1;
+ERROR HY000: Lost connection to server during query
+# Recovery must refuse the record, not apply it and notice later.
+FOUND 1 /Aria engine: Redo phase failed/ in mdev40498.err
+NOT FOUND /Table file is corrupted/ in mdev40498.err
+use mysqltest;
+#
+# The write side: a forged page offset pushes the copy past the page.
+#
+create table t2 (a int, b varchar(60), key(a), key(b))
+transactional=1 row_format=page engine=aria;
+set session debug_dbug="+d,corrupt_change_offset";
+select count(*) from t2;
+count(*)
+200
+set session debug_dbug="+d,maria_flush_whole_log,maria_crash";
+set global aria_checkpoint_interval=1;
+ERROR HY000: Lost connection to server during query
+FOUND 1 /Aria engine: Redo phase failed/ in mdev40498b.err
+NOT FOUND /Table file is corrupted/ in mdev40498b.err
+drop database mysqltest;
diff --git a/mysql-test/suite/maria/maria-recovery-corrupt-change.test b/mysql-test/suite/maria/maria-recovery-corrupt-change.test
new file mode 100644
index 0000000000000..6e45b4fe117de
--- /dev/null
+++ b/mysql-test/suite/maria/maria-recovery-corrupt-change.test
@@ -0,0 +1,129 @@
+# MDEV-40498: _ma_apply_redo_index() copied KEY_OP_CHANGE's logged length
+# without checking it against the end of the record, and bounded the write with
+# a DBUG_ASSERT, which release builds compile out.
+
+--source include/not_embedded.inc
+--source include/have_debug.inc
+--source include/have_maria.inc
+# the server is killed on purpose below
+--source include/not_valgrind.inc
+
+call mtr.add_suppression("File '.*aria_log.000.*' not found");
+
+let $MYSQLD_DATADIR= `select @@datadir`;
+let $MARIA_LOG=.;
+
+--disable_warnings
+drop database if exists mysqltest;
+--enable_warnings
+create database mysqltest;
+
+# the log is shared with earlier tests, and recovery below replays all of it
+connect (admin, localhost, root,,mysqltest,,);
+--enable_reconnect
+connection default;
+use mysqltest;
+--enable_reconnect
+--source include/maria_empty_logs.inc
+
+create table t1 (a int, b varchar(60), key(a), key(b))
+transactional=1 row_format=page engine=aria;
+
+# Forge the logged length of every KEY_OP_CHANGE below. The forged value is the
+# largest the page bound accepts, so the read bound is what refuses the record.
+set session debug_dbug="+d,corrupt_change_length";
+
+# Scattered keys so inserts land mid-page.
+--disable_query_log
+let $i= 40;
+while ($i)
+{
+  eval insert into t1 (a,b) values ($i*7919%10007,concat('v',$i*7)),($i*104729%10007,concat('w',$i*3)),($i*7919%9973,concat('x',$i*11)),($i*104729%9973,concat('y',$i*13)),($i*7919%9967,concat('z',$i*17));
+  dec $i;
+}
+--enable_query_log
+select count(*) from t1;
+
+# Kill without flushing pages, so recovery has to replay the forged records
+--write_line wait $MYSQLTEST_VARDIR/tmp/mysqld.1.expect
+set session debug_dbug="+d,maria_flush_whole_log,maria_crash";
+--error 2013
+set global aria_checkpoint_interval=1;
+
+--echo # Recovery must refuse the record, not apply it and notice later.
+# Failed recovery aborts the server, so --bootstrap drives it and exits itself
+--write_file $MYSQLTEST_VARDIR/tmp/mdev40498_boot.sql
+select 1;
+EOF
+
+--error 1
+--exec $MYSQLD_CMD --bootstrap --log-error=$MYSQLTEST_VARDIR/tmp/mdev40498.err < $MYSQLTEST_VARDIR/tmp/mdev40498_boot.sql > $MYSQLTEST_VARDIR/tmp/mdev40498.out 2>&1
+
+--let SEARCH_FILE= $MYSQLTEST_VARDIR/tmp/mdev40498.err
+--let SEARCH_PATTERN= Aria engine: Redo phase failed
+--source include/search_pattern_in_file.inc
+
+# Unfixed, the record is applied and the damage only shows up later.
+# Refusing it up front keeps this NOT FOUND.
+--let SEARCH_PATTERN= Table file is corrupted
+--source include/search_pattern_in_file.inc
+
+# every record in this log is forged, it can never be replayed
+--error 0,1
+remove_files_wildcard $MYSQLD_DATADIR aria_log.0*;
+
+--write_line restart $MYSQLTEST_VARDIR/tmp/mysqld.1.expect
+--enable_reconnect
+--source include/wait_until_connected_again.inc
+
+use mysqltest;
+
+--echo #
+--echo # The write side: a forged page offset pushes the copy past the page.
+--echo #
+
+create table t2 (a int, b varchar(60), key(a), key(b))
+transactional=1 row_format=page engine=aria;
+
+# The record stays length-consistent here, so the page bound is what refuses it.
+set session debug_dbug="+d,corrupt_change_offset";
+
+--disable_query_log
+let $i= 40;
+while ($i)
+{
+  eval insert into t2 (a,b) values ($i*7919%10007,concat('v',$i*7)),($i*104729%10007,concat('w',$i*3)),($i*7919%9973,concat('x',$i*11)),($i*104729%9973,concat('y',$i*13)),($i*7919%9967,concat('z',$i*17));
+  dec $i;
+}
+--enable_query_log
+select count(*) from t2;
+
+--write_line wait $MYSQLTEST_VARDIR/tmp/mysqld.1.expect
+set session debug_dbug="+d,maria_flush_whole_log,maria_crash";
+--error 2013
+set global aria_checkpoint_interval=1;
+
+--error 1
+--exec $MYSQLD_CMD --bootstrap --log-error=$MYSQLTEST_VARDIR/tmp/mdev40498b.err < $MYSQLTEST_VARDIR/tmp/mdev40498_boot.sql > $MYSQLTEST_VARDIR/tmp/mdev40498b.out 2>&1
+
+--let SEARCH_FILE= $MYSQLTEST_VARDIR/tmp/mdev40498b.err
+--let SEARCH_PATTERN= Aria engine: Redo phase failed
+--source include/search_pattern_in_file.inc
+
+--let SEARCH_PATTERN= Table file is corrupted
+--source include/search_pattern_in_file.inc
+
+--error 0,1
+remove_files_wildcard $MYSQLD_DATADIR aria_log.0*;
+
+--write_line restart $MYSQLTEST_VARDIR/tmp/mysqld.1.expect
+--enable_reconnect
+--source include/wait_until_connected_again.inc
+
+drop database mysqltest;
+
+remove_file $MYSQLTEST_VARDIR/tmp/mdev40498.err;
+remove_file $MYSQLTEST_VARDIR/tmp/mdev40498.out;
+remove_file $MYSQLTEST_VARDIR/tmp/mdev40498b.err;
+remove_file $MYSQLTEST_VARDIR/tmp/mdev40498b.out;
+remove_file $MYSQLTEST_VARDIR/tmp/mdev40498_boot.sql;
diff --git a/storage/maria/ma_key_recover.c b/storage/maria/ma_key_recover.c
index acec592b9227a..babb00f1b7bc6 100644
--- a/storage/maria/ma_key_recover.c
+++ b/storage/maria/ma_key_recover.c
@@ -567,7 +567,9 @@ my_bool _ma_log_add(MARIA_PAGE *ma_page,
   else
   {
     log_pos[0]= KEY_OP_OFFSET;
-    int2store(log_pos+1, offset);
+    int2store(log_pos+1,
+              (DBUG_IF("corrupt_change_offset") &&
+               (int) changed_length > move_length) ? current_size : offset);
     log_pos+= 3;
     if (move_length)
     {
@@ -600,7 +602,9 @@ my_bool _ma_log_add(MARIA_PAGE *ma_page,
     }
     log_pos[0]= KEY_OP_CHANGE;
   }
-  int2store(log_pos+1, changed_length);
+  int2store(log_pos+1, (log_pos[0] == KEY_OP_CHANGE &&
+                        DBUG_IF("corrupt_change_length")) ?
+                       current_size - offset : changed_length);
   log_pos+= 3;
 
   log_array[TRANSLOG_INTERNAL_PARTS + 0].str=    log_data;
@@ -1017,7 +1021,15 @@ uint _ma_apply_redo_index(MARIA_HA *info,
     {
       uint length= uint2korr(header);
       DBUG_PRINT("redo", ("key_op_change: %u", length));
-      DBUG_ASSERT(page_offset != 0 && page_offset + length <= page_length);
+
+      /* The data has to be inside the record and fit the used page */
+      if (unlikely((size_t) (header_end - header) < (size_t) length + 2 ||
+                   page_offset == 0 || page_offset + length > page_length))
+      {
+        DBUG_ASSERT(!maria_assert_if_crashed_table);
+        result= mark_crashed= 1;
+        goto err;
+      }
 
       memcpy(buff + page_offset, header + 2 , length);
       page_offset+= length;           /* Put offset after changed length */