diff --git a/app/vmselect/promql/eval.go b/app/vmselect/promql/eval.go
index 8bbfcb0c1..9526cca2e 100644
--- a/app/vmselect/promql/eval.go
+++ b/app/vmselect/promql/eval.go
@@ -764,10 +764,7 @@ func getRollupMemoryLimiter() *memoryLimiter {
 func evalRollupWithIncrementalAggregate(name string, iafc *incrementalAggrFuncContext, rss *netstorage.Results, rcs []*rollupConfig,
 	preFunc func(values []float64, timestamps []int64), sharedTimestamps []int64, removeMetricGroup bool) ([]*timeseries, error) {
 	err := rss.RunParallel(func(rs *netstorage.Result, workerID uint) error {
-		if name != "default_rollup" {
-			// Remove Prometheus staleness marks, so non-default rollup functions don't hit NaN values.
-			rs.Values, rs.Timestamps = dropStaleNaNs(rs.Values, rs.Timestamps)
-		}
+		rs.Values, rs.Timestamps = dropStaleNaNs(name, rs.Values, rs.Timestamps)
 		preFunc(rs.Values, rs.Timestamps)
 		ts := getTimeseries()
 		defer putTimeseries(ts)
@@ -801,10 +798,7 @@ func evalRollupNoIncrementalAggregate(name string, rss *netstorage.Results, rcs
 	tss := make([]*timeseries, 0, rss.Len()*len(rcs))
 	var tssLock sync.Mutex
 	err := rss.RunParallel(func(rs *netstorage.Result, workerID uint) error {
-		if name != "default_rollup" {
-			// Remove Prometheus staleness marks, so non-default rollup functions don't hit NaN values.
-			rs.Values, rs.Timestamps = dropStaleNaNs(rs.Values, rs.Timestamps)
-		}
+		rs.Values, rs.Timestamps = dropStaleNaNs(name, rs.Values, rs.Timestamps)
 		preFunc(rs.Values, rs.Timestamps)
 		for _, rc := range rcs {
 			if tsm := newTimeseriesMap(name, sharedTimestamps, &rs.MetricName); tsm != nil {
@@ -901,7 +895,13 @@ func toTagFilter(dst *storage.TagFilter, src *metricsql.LabelFilter) {
 	dst.IsNegative = src.IsNegative
 }
 
-func dropStaleNaNs(values []float64, timestamps []int64) ([]float64, []int64) {
+func dropStaleNaNs(name string, values []float64, timestamps []int64) ([]float64, []int64) {
+	if name == "default_rollup" {
+		// Do not drop Prometheus staleness marks (aka stale NaNs) for default_rollup() function,
+		// since it uses them for Prometheus-style staleness detection.
+		return values, timestamps
+	}
+	// Remove Prometheus staleness marks, so non-default rollup functions don't hit NaN values.
 	hasStaleSamples := false
 	for _, v := range values {
 		if decimal.IsStaleNaN(v) {