diff --git a/app/vmselect/promql/binary_op.go b/app/vmselect/promql/binary_op.go
index d258d6330..b103b2075 100644
--- a/app/vmselect/promql/binary_op.go
+++ b/app/vmselect/promql/binary_op.go
@@ -267,6 +267,12 @@ func mergeNonOverlappingTimeseries(dst, src *timeseries) bool {
 	if overlaps > 2 {
 		return false
 	}
+	// Do not merge time series with too small number of datapoints.
+	// This can be the case during evaluation of instant queries (alerting or recording rules).
+	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1141
+	if len(srcValues) <= 2 && len(dstValues) <= 2 {
+		return false
+	}
 	// Time series can be merged. Merge them.
 	for i, v := range srcValues {
 		if math.IsNaN(v) {
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index ace1d4f6a..22727f9d2 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -14,6 +14,7 @@
 
 * BUGFIX: prevent from infinite loop on `{__graphite__="..."}` filters when a metric name contains `*`, `{` or `[` chars.
 * BUGFIX: prevent from infinite loop in `/metrics/find` and `/metrics/expand` [Graphite Metrics API handlers](https://victoriametrics.github.io/#graphite-metrics-api-usage) when they match metric names or labels with `*`, `{` or `[` chars.
+* BUGFIX: do not merge duplicate time series during requests to `/api/v1/query`. See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1141
 
 
 # [v1.56.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.56.0)