diff --git a/airflow-core/src/airflow/api_fastapi/core_api/datamodels/dag_run.py b/airflow-core/src/airflow/api_fastapi/core_api/datamodels/dag_run.py
index 56546b58996c9..261fc8e88d3c1 100644
--- a/airflow-core/src/airflow/api_fastapi/core_api/datamodels/dag_run.py
+++ b/airflow-core/src/airflow/api_fastapi/core_api/datamodels/dag_run.py
@@ -126,10 +126,7 @@ def validate_context(self, dag: SerializedDAG) -> dict:
                     end=timezone.coerce_datetime(self.data_interval_end),
                 )
             else:
-                data_interval = dag.timetable.infer_manual_data_interval(
-                    run_after=coerced_logical_date or timezone.coerce_datetime(run_after)
-                )
-                run_after = data_interval.end
+                data_interval = dag.timetable.infer_manual_data_interval(run_after=coerced_logical_date)
 
         run_id = self.dag_run_id or dag.timetable.generate_run_id(
             run_type=DagRunType.MANUAL,
diff --git a/airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_dag_run.py b/airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_dag_run.py
index 785904d3d8100..897ca2bfceb1a 100644
--- a/airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_dag_run.py
+++ b/airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_dag_run.py
@@ -1883,6 +1883,41 @@ def test_should_respond_200_with_null_logical_date(self, test_client):
             "partition_key": None,
         }
 
+    @pytest.mark.usefixtures("configure_git_connection_for_dag_bundle")
+    def test_should_generate_unique_run_id_for_scheduled_dag(self, dag_maker, test_client, session):
+        "Ensure manual triggers on scheduled DAGs don't conflict on run_id"
+        scheduled_dag_id = "test_scheduled_dag"
+        with dag_maker(
+            dag_id=scheduled_dag_id,
+            schedule="@daily",
+            start_date=START_DATE1,
+            session=session,
+            serialized=True,
+        ):
+            EmptyOperator(task_id="test_task")
+
+        session.commit()
+
+        response_1 = test_client.post(
+            f"/dags/{scheduled_dag_id}/dagRuns",
+            json={
+                "logical_date": "2025-12-11T16:00:00+00:00",
+                "run_after": "2025-12-11T16:00:00+00:00",
+            },
+        )
+        assert response_1.status_code == 200
+
+        response_2 = test_client.post(
+            f"/dags/{scheduled_dag_id}/dagRuns",
+            json={
+                "logical_date": "2025-12-11T16:01:00+00:00",
+                "run_after": "2025-12-11T16:01:00+00:00",
+            },
+        )
+        assert response_2.status_code == 200
+
+        assert response_1.json()["dag_run_id"] != response_2.json()["dag_run_id"]
+
     @time_machine.travel("2025-10-02 12:00:00", tick=False)
     @pytest.mark.usefixtures("custom_timetable_plugin")
     def test_custom_timetable_generate_run_id_for_manual_trigger(self, dag_maker, test_client, session):