diff --git a/crates/fidc-core/src/data.rs b/crates/fidc-core/src/data.rs
index d35a4a8..1b3ccf4 100644
--- a/crates/fidc-core/src/data.rs
+++ b/crates/fidc-core/src/data.rs
@@ -623,6 +623,7 @@ struct SymbolDailySeriesBase {
     upper_limits: Vec<f64>,
     lower_limits: Vec<f64>,
     price_ticks: Vec<f64>,
+    day_open_prefix: Vec<f64>,
     open_prefix: Vec<f64>,
     close_prefix: Vec<f64>,
     prev_close_prefix: Vec<f64>,
@@ -880,6 +881,7 @@ impl SymbolPriceSeries {
             lower_limits.push(row.lower_limit);
             price_ticks.push(row.price_tick);
         }
+        let day_open_prefix = prefix_sums(&day_opens);
         let open_prefix = prefix_sums(&opens);
         let close_prefix = prefix_sums(&closes);
         let prev_close_prefix = prefix_sums(&prev_closes);
@@ -926,6 +928,7 @@ impl SymbolPriceSeries {
                 upper_limits,
                 lower_limits,
                 price_ticks,
+                day_open_prefix,
                 open_prefix,
                 close_prefix,
                 prev_close_prefix,
@@ -1205,7 +1208,7 @@ impl SymbolPriceSeries {
 
     fn prefix_for(&self, field: PriceField) -> &[f64] {
         match field {
-            PriceField::DayOpen => &self.open_prefix,
+            PriceField::DayOpen => &self.day_open_prefix,
             PriceField::Open => &self.open_prefix,
             PriceField::Close => &self.close_prefix,
             PriceField::Last => &self.last_prefix,
@@ -6553,6 +6556,24 @@ mod tests {
         }
     }
 
+    #[test]
+    fn day_open_moving_average_uses_its_own_historical_column() {
+        let mut first = market_row("2025-01-02", 10.0, 100);
+        first.day_open = 10.0;
+        first.open = 20.0;
+        let mut second = market_row("2025-01-03", 12.0, 200);
+        second.day_open = 12.0;
+        second.open = 24.0;
+        let rows = [first, second];
+        let series = SymbolPriceSeries::new("000001.SZ".to_string(), &rows);
+        let date = NaiveDate::from_ymd_opt(2025, 1, 3).unwrap();
+        assert_eq!(series.trailing_values(date, 2, PriceField::DayOpen), vec![10.0, 12.0]);
+        assert_eq!(series.moving_average(date, 2, PriceField::DayOpen), Some(11.0));
+        assert_eq!(series.moving_average(date, 2, PriceField::Open), Some(22.0));
+        assert_eq!(series.moving_average(date, 0, PriceField::DayOpen), None);
+        assert_eq!(series.moving_average(date, 3, PriceField::DayOpen), None);
+    }
+
     #[test]
     fn symbol_price_series_test_constructor_sorts_unsorted_rows() {
         let series = SymbolPriceSeries::new(