diff --git a/app/vmselect/promql/binary_op.go b/app/vmselect/promql/binary_op.go
index a4884c748..fcc2f4250 100644
--- a/app/vmselect/promql/binary_op.go
+++ b/app/vmselect/promql/binary_op.go
@@ -296,9 +296,13 @@ func adjustBinaryOpTags(be *binaryOpExpr, left, right []*timeseries) ([]*timeser
 		if len(tss) == 1 {
 			return nil
 		}
+		if mergeNonOverlappingTimeseries(tss) {
+			return nil
+		}
 		return fmt.Errorf(`duplicate timeseries on the %s side of %s %s: %s and %s`, side, be.Op, be.GroupModifier.AppendString(nil),
 			stringMetricTags(&tss[0].MetricName), stringMetricTags(&tss[1].MetricName))
 	}
+
 	var rvsLeft, rvsRight []*timeseries
 	mLeft, mRight := createTimeseriesMapByTagSet(be, left, right)
 	joinOp := strings.ToLower(be.JoinModifier.Op)
@@ -498,3 +502,26 @@ func isScalar(arg []*timeseries) bool {
 	}
 	return len(mn.Tags) == 0
 }
+
+func mergeNonOverlappingTimeseries(tss []*timeseries) bool {
+	if len(tss) < 2 {
+		logger.Panicf("BUG: expecting at least two timeseries. Got %d", len(tss))
+	}
+
+	// Check whether time series in tss overlap.
+	var dst timeseries
+	dst.CopyFromShallowTimestamps(tss[0])
+	dstValues := dst.Values
+	for _, ts := range tss[1:] {
+		for i, value := range ts.Values {
+			if math.IsNaN(dstValues[i]) {
+				dstValues[i] = value
+			} else if !math.IsNaN(value) {
+				// Time series overlap.
+				return false
+			}
+		}
+	}
+	tss[0].CopyFromShallowTimestamps(&dst)
+	return true
+}
diff --git a/app/vmselect/promql/exec_test.go b/app/vmselect/promql/exec_test.go
index 99816421d..e53eba23f 100644
--- a/app/vmselect/promql/exec_test.go
+++ b/app/vmselect/promql/exec_test.go
@@ -1739,6 +1739,24 @@ func TestExecSuccess(t *testing.T) {
 		resultExpected := []netstorage.Result{r}
 		f(q, resultExpected)
 	})
+	t.Run(`vector * on(foo) group_left() duplicate_timeseries`, func(t *testing.T) {
+		t.Parallel()
+		q := `label_set(time()/10, "foo", "bar") + on(foo) group_left() (
+			label_set(time() < 1400, "foo", "bar", "op", "le"),
+			label_set(time() >= 1400, "foo", "bar", "op", "ge"),
+		)`
+		r1 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{1100, 1320, 1540, 1760, 1980, 2200},
+			Timestamps: timestampsExpected,
+		}
+		r1.MetricName.Tags = []storage.Tag{{
+			Key:   []byte("foo"),
+			Value: []byte("bar"),
+		}}
+		resultExpected := []netstorage.Result{r1}
+		f(q, resultExpected)
+	})
 	t.Run(`vector * on() group_left scalar`, func(t *testing.T) {
 		t.Parallel()
 		q := `sort_desc((label_set(time(), "foo", "bar") or label_set(10, "foo", "qwert")) * on() group_left 2)`
@@ -3594,10 +3612,12 @@ func TestExecError(t *testing.T) {
 	f(`1 + group_left() (label_set(1, "foo", bar"), label_set(2, "foo", "baz"))`)
 	f(`1 + on() group_left() (label_set(1, "foo", bar"), label_set(2, "foo", "baz"))`)
 	f(`1 + on(a) group_left(b) (label_set(1, "foo", bar"), label_set(2, "foo", "baz"))`)
+	f(`label_set(1, "foo", "bar") + on(foo) group_left() (label_set(1, "foo", "bar", "a", "b"), label_set(1, "foo", "bar", "a", "c"))`)
 	f(`(label_set(1, "foo", bar"), label_set(2, "foo", "baz")) + group_right 1`)
 	f(`(label_set(1, "foo", bar"), label_set(2, "foo", "baz")) + on() group_right 1`)
 	f(`(label_set(1, "foo", bar"), label_set(2, "foo", "baz")) + on(a) group_right(b,c) 1`)
 	f(`(label_set(1, "foo", bar"), label_set(2, "foo", "baz")) + on() 1`)
+	f(`(label_set(1, "foo", "bar", "a", "b"), label_set(1, "foo", "bar", "a", "c")) + on(foo) group_right() label_set(1, "foo", "bar")`)
 	f(`1 + on() (label_set(1, "foo", bar"), label_set(2, "foo", "baz"))`)
 
 	// With expressions