diff --git a/mysql-test/suite/innodb_fts/r/innodb_fts_misc.result b/mysql-test/suite/innodb_fts/r/innodb_fts_misc.result
index 1322867551f..bc9548b7d8e 100644
--- a/mysql-test/suite/innodb_fts/r/innodb_fts_misc.result
+++ b/mysql-test/suite/innodb_fts/r/innodb_fts_misc.result
@@ -1384,3 +1384,8 @@ SELECT * FROM t1 WHERE MATCH (a) AGAINST ('+"good database"' IN BOOLEAN MODE);
 id	a
 1	know mysql good database
 DROP TABLE t1;
+CREATE TABLE t1(f1 TEXT, FULLTEXT KEY(f1))ENGINE=InnoDB;
+INSERT INTO t1 VALUES(repeat("this is the test case", 500));
+ALTER TABLE t1 KEY_BLOCK_SIZE=4;
+ALTER TABLE t1 KEY_BLOCK_SIZE=0;
+DROP TABLE t1;
diff --git a/mysql-test/suite/innodb_fts/t/innodb_fts_misc.test b/mysql-test/suite/innodb_fts/t/innodb_fts_misc.test
index 150d632b26f..6fa4f25c60e 100644
--- a/mysql-test/suite/innodb_fts/t/innodb_fts_misc.test
+++ b/mysql-test/suite/innodb_fts/t/innodb_fts_misc.test
@@ -1331,3 +1331,11 @@ INSERT INTO t1 (a) VALUES
 SELECT * FROM t1 WHERE MATCH (a) AGAINST ('+"good database"' IN BOOLEAN MODE);
 
 DROP TABLE t1;
+
+# MDEV-19974 InnoDB: Cannot load compressed BLOB
+CREATE TABLE t1(f1 TEXT, FULLTEXT KEY(f1))ENGINE=InnoDB;
+INSERT INTO t1 VALUES(repeat("this is the test case", 500));
+ALTER TABLE t1 KEY_BLOCK_SIZE=4;
+ALTER TABLE t1 KEY_BLOCK_SIZE=0;
+DROP TABLE t1;
+
diff --git a/storage/innobase/include/row0ftsort.h b/storage/innobase/include/row0ftsort.h
index b2c5651c9c5..b735576fbbb 100644
--- a/storage/innobase/include/row0ftsort.h
+++ b/storage/innobase/include/row0ftsort.h
@@ -59,6 +59,8 @@ struct fts_psort_t;
 struct fts_psort_common_t {
 	row_merge_dup_t*	dup;		/*!< descriptor of FTS index */
 	dict_table_t*		new_table;	/*!< source table */
+	/* Old table page size */
+	page_size_t		old_page_size;
 	trx_t*			trx;		/*!< transaction */
 	fts_psort_t*		all_info;	/*!< all parallel sort info */
 	os_event_t		sort_event;	/*!< sort event */
@@ -190,26 +192,27 @@ row_merge_create_fts_sort_index(
 				instead of 8 bytes integer to
 				store Doc ID during sort */
 
-/********************************************************************//**
-Initialize FTS parallel sort structures.
+/** Initialize FTS parallel sort structures.
+@param[in]	trx		transaction
+@param[in,out]	dup		descriptor of FTS index being created
+@param[in]	new_table	table where indexes are created
+@param[in]	opt_doc_id_size	whether to use 4 bytes instead of 8 bytes
+				integer to store Doc ID during sort
+@param[in]	old_page_size	page size of the old table during alter
+@param[out]	psort		parallel sort info to be instantiated
+@param[out]	merge		parallel merge info to be instantiated
 @return TRUE if all successful */
 ibool
 row_fts_psort_info_init(
-/*====================*/
-	trx_t*			trx,	/*!< in: transaction */
-	row_merge_dup_t*	dup,	/*!< in,own: descriptor of
-					FTS index being created */
-	const dict_table_t*	new_table,/*!< in: table where indexes are
-					created */
+	trx_t*			trx,
+	row_merge_dup_t*	dup,
+	const dict_table_t*	new_table,
 	ibool			opt_doc_id_size,
-					/*!< in: whether to use 4 bytes
-					instead of 8 bytes integer to
-					store Doc ID during sort */
-	fts_psort_t**		psort,	/*!< out: parallel sort info to be
-					instantiated */
-	fts_psort_t**		merge)	/*!< out: parallel merge info
-					to be instantiated */
+	const page_size_t	old_page_size,
+	fts_psort_t**		psort,
+	fts_psort_t**		merge)
 	MY_ATTRIBUTE((nonnull));
+
 /********************************************************************//**
 Clean up and deallocate FTS parallel sort structures, and close
 temparary merge sort files */
diff --git a/storage/innobase/row/row0ftsort.cc b/storage/innobase/row/row0ftsort.cc
index e8ffabca142..f40d6772536 100644
--- a/storage/innobase/row/row0ftsort.cc
+++ b/storage/innobase/row/row0ftsort.cc
@@ -159,25 +159,26 @@ row_merge_create_fts_sort_index(
 
 	return(new_index);
 }
-/*********************************************************************//**
-Initialize FTS parallel sort structures.
+
+/** Initialize FTS parallel sort structures.
+@param[in]	trx		transaction
+@param[in,out]	dup		descriptor of FTS index being created
+@param[in]	new_table	table where indexes are created
+@param[in]	opt_doc_id_size	whether to use 4 bytes instead of 8 bytes
+				integer to store Doc ID during sort
+@param[in]	old_page_size	page size of the old table during alter
+@param[out]	psort		parallel sort info to be instantiated
+@param[out]	merge		parallel merge info to be instantiated
 @return TRUE if all successful */
 ibool
 row_fts_psort_info_init(
-/*====================*/
-	trx_t*			trx,	/*!< in: transaction */
-	row_merge_dup_t*	dup,	/*!< in,own: descriptor of
-					FTS index being created */
-	const dict_table_t*	new_table,/*!< in: table on which indexes are
-					created */
-	ibool			opt_doc_id_size,
-					/*!< in: whether to use 4 bytes
-					instead of 8 bytes integer to
-					store Doc ID during sort */
-	fts_psort_t**		psort,	/*!< out: parallel sort info to be
-					instantiated */
-	fts_psort_t**		merge)	/*!< out: parallel merge info
-					to be instantiated */
+        trx_t*                  trx,
+        row_merge_dup_t*        dup,
+        const dict_table_t*     new_table,
+        ibool                   opt_doc_id_size,
+        const page_size_t       old_page_size,
+        fts_psort_t**           psort,
+        fts_psort_t**           merge)
 {
 	ulint			i;
 	ulint			j;
@@ -210,6 +211,7 @@ row_fts_psort_info_init(
 
 	common_info->dup = dup;
 	common_info->new_table = (dict_table_t*) new_table;
+	common_info->old_page_size = old_page_size;
 	common_info->trx = trx;
 	common_info->all_info = psort_info;
 	common_info->sort_event = os_event_create(0);
@@ -803,7 +805,8 @@ DECLARE_THREAD(fts_parallel_tokenization)(
 	block = psort_info->merge_block;
 	crypt_block = psort_info->crypt_block;
 
-	const page_size_t&	page_size = dict_table_page_size(table);
+	const page_size_t	old_page_size =
+			psort_info->psort_common->old_page_size;
 
 	row_merge_fts_get_next_doc_item(psort_info, &doc_item);
 
@@ -833,7 +836,7 @@ loop:
 				doc.text.f_str =
 					btr_copy_externally_stored_field(
 						&doc.text.f_len, data,
-						page_size, data_len, blob_heap);
+						old_page_size, data_len, blob_heap);
 			} else {
 				doc.text.f_str = data;
 				doc.text.f_len = data_len;
diff --git a/storage/innobase/row/row0merge.cc b/storage/innobase/row/row0merge.cc
index fa85a511ba6..73d4a836d98 100644
--- a/storage/innobase/row/row0merge.cc
+++ b/storage/innobase/row/row0merge.cc
@@ -4678,6 +4678,7 @@ row_merge_build_indexes(
 			created */
 			if (!row_fts_psort_info_init(
 					trx, dup, new_table, opt_doc_id_size,
+					dict_table_page_size(old_table),
 					&psort_info, &merge_info)) {
 				error = DB_CORRUPTION;
 				goto func_exit;