diff --git a/system-variables.md b/system-variables.md
index d711456de897..3091028f1c28 100644
--- a/system-variables.md
+++ b/system-variables.md
@@ -2421,8 +2421,9 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
 - Persists to cluster: Yes
 - Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
 - Type: Boolean
-- Default value: `OFF`
-- This variable controls whether Index Join is supported when the inner table has `Selection` or `Projection` operators on it. The default value `OFF` means that Index Join is not supported in this scenario.
+- Default value: `ON`. The default value is `OFF` for v8.3.0 and earlier versions.
+- This variable controls whether Index Join is supported when the inner table has `Selection`, `Aggregation`, or `Projection` operators on it. The default value `OFF` means that Index Join is not supported in this scenario.
+- If you upgrade your TiDB cluster from a version earlier than v7.0.0 to v8.4.0 or later, this variable is set to `OFF` by default, indicating that Index Join is not supported in this scenario.
 
 ### tidb_enable_ordered_result_mode