diff --git a/src/frontend/planner_test/tests/testdata/input/agg.yaml b/src/frontend/planner_test/tests/testdata/input/agg.yaml
index 75aa7249accce..9310a826a691e 100644
--- a/src/frontend/planner_test/tests/testdata/input/agg.yaml
+++ b/src/frontend/planner_test/tests/testdata/input/agg.yaml
@@ -1070,6 +1070,13 @@
   expected_outputs:
     - logical_plan
     - stream_plan
+- name: test approx_percentile hash_agg forced should use single phase agg
+  sql: |
+    SET RW_FORCE_TWO_PHASE_AGG=true;
+    create table t (v1 int, grp_col int);
+    select approx_percentile(0.5, 0.01) WITHIN GROUP (order by v1) from t group by grp_col;
+  expected_outputs:
+    - stream_error
 - name: test approx percentile with default relative_error
   sql: |
     CREATE TABLE t (v1 int);
diff --git a/src/frontend/planner_test/tests/testdata/output/agg.yaml b/src/frontend/planner_test/tests/testdata/output/agg.yaml
index 9fd70f1fb28fd..97d440b64df12 100644
--- a/src/frontend/planner_test/tests/testdata/output/agg.yaml
+++ b/src/frontend/planner_test/tests/testdata/output/agg.yaml
@@ -2103,6 +2103,14 @@
           └─StreamHashAgg { group_key: [$expr5], aggs: [sum(t.v1), count, max(t.v2)] }
             └─StreamProject { exprs: [t.v1, t.v1::Float64 as $expr3, t.v2, t.v2::Float64 as $expr4, t._row_id, Vnode(t._row_id) as $expr5] }
               └─StreamTableScan { table: t, columns: [t.v1, t.v2, t._row_id], stream_scan_type: ArrangementBackfill, stream_key: [t._row_id], pk: [_row_id], dist: UpstreamHashShard(t._row_id) }
+- name: test approx_percentile hash_agg forced should use single phase agg
+  sql: |
+    SET RW_FORCE_TWO_PHASE_AGG=true;
+    create table t (v1 int, grp_col int);
+    select approx_percentile(0.5, 0.01) WITHIN GROUP (order by v1) from t group by grp_col;
+  stream_error: |-
+    Feature is not yet implemented: two-phase streaming approx percentile aggregation with group key, please use single phase aggregation instead
+    No tracking issue yet. Feel free to submit a feature request at https://github.com/risingwavelabs/risingwave/issues/new?labels=type%2Ffeature&template=feature_request.yml
 - name: test approx percentile with default relative_error
   sql: |
     CREATE TABLE t (v1 int);
diff --git a/src/frontend/src/optimizer/plan_node/logical_agg.rs b/src/frontend/src/optimizer/plan_node/logical_agg.rs
index e63b7d760a68f..cf7025be90872 100644
--- a/src/frontend/src/optimizer/plan_node/logical_agg.rs
+++ b/src/frontend/src/optimizer/plan_node/logical_agg.rs
@@ -311,7 +311,10 @@ impl LogicalAgg {
             col_mapping: approx_percentile_col_mapping,
         } = approx;
         if !self.group_key().is_empty() && !approx_percentile_agg_calls.is_empty() {
-            bail_not_implemented!("two-phase approx percentile agg with group key, please use single phase agg for approx_percentile with group key");
+            bail_not_implemented!(
+                "two-phase streaming approx percentile aggregation with group key, \
+             please use single phase aggregation instead"
+            );
         }
 
         // Either we have approx percentile aggs and non_approx percentile aggs,