diff --git a/mysql-test/suite/sys_vars/r/sysvars_innodb.result b/mysql-test/suite/sys_vars/r/sysvars_innodb.result
index 79d24242435..1808cfb6ea3 100644
--- a/mysql-test/suite/sys_vars/r/sysvars_innodb.result
+++ b/mysql-test/suite/sys_vars/r/sysvars_innodb.result
@@ -642,6 +642,18 @@ NUMERIC_BLOCK_SIZE	NULL
 ENUM_VALUE_LIST	OFF,ON
 READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
+VARIABLE_NAME	INNODB_DEBUG_SYNC
+SESSION_VALUE	NULL
+DEFAULT_VALUE	
+VARIABLE_SCOPE	GLOBAL
+VARIABLE_TYPE	VARCHAR
+VARIABLE_COMMENT	debug_sync for innodb purge threads. Use it to set up sync points for all purge threads at once. The commands will be applied sequentially at the beginning of purging the next undo record.
+NUMERIC_MIN_VALUE	NULL
+NUMERIC_MAX_VALUE	NULL
+NUMERIC_BLOCK_SIZE	NULL
+ENUM_VALUE_LIST	NULL
+READ_ONLY	NO
+COMMAND_LINE_ARGUMENT	NONE
 VARIABLE_NAME	INNODB_DEFAULT_ENCRYPTION_KEY_ID
 SESSION_VALUE	1
 DEFAULT_VALUE	1
diff --git a/storage/innobase/handler/ha_innodb.cc b/storage/innobase/handler/ha_innodb.cc
index df8e0c5ee10..a18b6215417 100644
--- a/storage/innobase/handler/ha_innodb.cc
+++ b/storage/innobase/handler/ha_innodb.cc
@@ -21015,9 +21015,9 @@ char *innobase_debug_sync;
 static MYSQL_SYSVAR_STR(debug_sync, innobase_debug_sync,
 			PLUGIN_VAR_NOCMDARG,
 			"debug_sync for innodb purge threads. "
-			"Use it t oset up sync points for all purge threads "
+			"Use it to set up sync points for all purge threads "
 			"at once. The commands will be applied sequentially at "
-			"the beginning of purging the next node ",
+			"the beginning of purging the next undo record.",
 			NULL,
 			innobase_debug_sync_set, NULL);
 #endif /* UNIV_DEBUG */
diff --git a/storage/innobase/include/que0que.h b/storage/innobase/include/que0que.h
index 3e23978f54c..8489551e64d 100644
--- a/storage/innobase/include/que0que.h
+++ b/storage/innobase/include/que0que.h
@@ -386,8 +386,8 @@ struct que_thr_t{
 	row_prebuilt_t*	prebuilt;	/*!< prebuilt structure processed by
 					the query thread */
 
-	ut_d(srv_slot_t *thread_slot;)	/*!< a slot from srv_sys.sys_threads
- * 					if any */
+	/** a slot of srv_sys.sys_threads, for DEBUG_SYNC in purge thread */
+	ut_d(srv_slot_t* thread_slot;)
 };
 
 #define QUE_THR_MAGIC_N		8476583
diff --git a/storage/innobase/que/que0que.cc b/storage/innobase/que/que0que.cc
index 96f90d63759..1d3d1573299 100644
--- a/storage/innobase/que/que0que.cc
+++ b/storage/innobase/que/que0que.cc
@@ -1082,9 +1082,6 @@ que_run_threads_low(
 	ut_a(thr_get_trx(thr)->error_state == DB_SUCCESS);
 	ut_ad(!trx_mutex_own(thr_get_trx(thr)));
 
-	/* slot can be received from purge thread for debug_sync setup */
-	ut_d(srv_slot_t *slot = thr->thread_slot);
-
 	/* cumul_resource counts how much resources the OS thread (NOT the
 	query thread) has spent in this function */
 
diff --git a/storage/innobase/srv/srv0srv.cc b/storage/innobase/srv/srv0srv.cc
index 16efe4a6a34..42e026df7e4 100644
--- a/storage/innobase/srv/srv0srv.cc
+++ b/storage/innobase/srv/srv0srv.cc
@@ -3047,18 +3047,18 @@ srv_was_tablespace_truncated(const fil_space_t* space)
 }
 
 #ifdef UNIV_DEBUG
-static uint get_first_slot(srv_thread_type type)
+static ulint get_first_slot(srv_thread_type type)
 {
 	switch (type) {
-		case SRV_MASTER:
-			return SRV_MASTER_SLOT;
-		case SRV_PURGE:
-			return SRV_PURGE_SLOT;
-		case SRV_WORKER:
-			/* Find an empty slot, skip the master and purge slots. */
-			return SRV_WORKER_SLOTS_START;
-		default:
-			ut_error;
+	case SRV_MASTER:
+		return SRV_MASTER_SLOT;
+	case SRV_PURGE:
+		return SRV_PURGE_SLOT;
+	case SRV_WORKER:
+		/* Find an empty slot, skip the master and purge slots. */
+		return SRV_WORKER_SLOTS_START;
+	default:
+		ut_error;
 	}
 }
 
@@ -3066,14 +3066,12 @@ void srv_for_each_thread(srv_thread_type type,
 			 srv_slot_callback_t callback,
 			 const void *arg)
 {
-	int slot_idx= get_first_slot(type);
-	while(slot_idx < srv_sys.n_sys_threads
-	      && srv_sys.sys_threads[slot_idx].in_use
-	      && srv_sys.sys_threads[slot_idx].type == type)
-	{
-		srv_slot_t *slot= &srv_sys.sys_threads[slot_idx];
-		callback(slot, arg);
-		slot_idx++;
+	for (ulint slot_idx= get_first_slot(type);
+	     slot_idx < srv_sys.n_sys_threads
+		     && srv_sys.sys_threads[slot_idx].in_use
+		     && srv_sys.sys_threads[slot_idx].type == type;
+	     slot_idx++) {
+		callback(&srv_sys.sys_threads[slot_idx], arg);
 	}
 }
 #endif