diff --git a/mysql-test/suite/innodb_zip/r/blob.result b/mysql-test/suite/innodb_zip/r/blob.result
new file mode 100644
index 00000000000..bfe96b8a869
--- /dev/null
+++ b/mysql-test/suite/innodb_zip/r/blob.result
@@ -0,0 +1,21 @@
+#
+# MDEV-21259 Assertion 'w != NORMAL || mach_read_from_4(ptr) != val'
+# failed in mtr_t::write(), btr_free_externally_stored_field()
+#
+SET @saved_frequency = @@GLOBAL.innodb_purge_rseg_truncate_frequency;
+SET GLOBAL innodb_purge_rseg_truncate_frequency = 1;
+CREATE TABLE t1 (c TEXT, f2 INT PRIMARY KEY, f3 INT UNIQUE)
+ENGINE=InnoDB ROW_FORMAT=COMPRESSED KEY_BLOCK_SIZE=4;
+SET @level= @@GLOBAL.innodb_compression_level;
+SET GLOBAL innodb_compression_level=0;
+connect  prevent_purge,localhost,root;
+START TRANSACTION WITH CONSISTENT SNAPSHOT;
+connection default;
+INSERT INTO t1 VALUES('a',1,0);
+UPDATE t1 SET c= REPEAT('a b ',4096);
+REPLACE INTO t1 SELECT * FROM t1;
+disconnect prevent_purge;
+InnoDB		0 transactions not purged
+DROP TABLE t1;
+SET GLOBAL innodb_compression_level = @level;
+SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;
diff --git a/mysql-test/suite/innodb_zip/t/blob.test b/mysql-test/suite/innodb_zip/t/blob.test
new file mode 100644
index 00000000000..b85cf7313d0
--- /dev/null
+++ b/mysql-test/suite/innodb_zip/t/blob.test
@@ -0,0 +1,29 @@
+--source include/innodb_page_size_small.inc
+
+--echo #
+--echo # MDEV-21259 Assertion 'w != NORMAL || mach_read_from_4(ptr) != val'
+--echo # failed in mtr_t::write(), btr_free_externally_stored_field()
+--echo #
+
+SET @saved_frequency = @@GLOBAL.innodb_purge_rseg_truncate_frequency;
+SET GLOBAL innodb_purge_rseg_truncate_frequency = 1;
+
+CREATE TABLE t1 (c TEXT, f2 INT PRIMARY KEY, f3 INT UNIQUE)
+ENGINE=InnoDB ROW_FORMAT=COMPRESSED KEY_BLOCK_SIZE=4;
+
+SET @level= @@GLOBAL.innodb_compression_level;
+SET GLOBAL innodb_compression_level=0;
+--connect (prevent_purge,localhost,root)
+START TRANSACTION WITH CONSISTENT SNAPSHOT;
+
+--connection default
+INSERT INTO t1 VALUES('a',1,0);
+UPDATE t1 SET c= REPEAT('a b ',4096);
+REPLACE INTO t1 SELECT * FROM t1;
+
+--disconnect prevent_purge
+--source ../../innodb/include/wait_all_purged.inc
+
+DROP TABLE t1;
+SET GLOBAL innodb_compression_level = @level;
+SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;
diff --git a/storage/innobase/btr/btr0cur.cc b/storage/innobase/btr/btr0cur.cc
index 932072ad182..cf3d0839e86 100644
--- a/storage/innobase/btr/btr0cur.cc
+++ b/storage/innobase/btr/btr0cur.cc
@@ -8110,9 +8110,9 @@ btr_free_externally_stored_field(
 				mtr.write<4>(*block,
 					     BTR_EXTERN_PAGE_NO + field_ref,
 					     next_page_no);
-				mtr.write<4>(*block,
-					     BTR_EXTERN_LEN + 4 + field_ref,
-					     0U);
+				mtr.write<4,mtr_t::OPT>(*block,
+							BTR_EXTERN_LEN + 4
+							+ field_ref, 0U);
 			}
 		} else {
 			ut_ad(!block->page.zip.data);