diff --git a/tsdb/index/postings.go b/tsdb/index/postings.go
index a2c5a8223..538413383 100644
--- a/tsdb/index/postings.go
+++ b/tsdb/index/postings.go
@@ -660,7 +660,7 @@ func (it *intersectPostings) Err() error {
 }
 
 // Merge returns a new iterator over the union of the input iterators.
-func Merge(_ context.Context, its ...Postings) Postings {
+func Merge[T Postings](_ context.Context, its ...T) Postings {
 	if len(its) == 0 {
 		return EmptyPostings()
 	}
@@ -675,19 +675,19 @@ func Merge(_ context.Context, its ...Postings) Postings {
 	return p
 }
 
-type mergedPostings struct {
-	p   []Postings
-	h   *loser.Tree[storage.SeriesRef, Postings]
+type mergedPostings[T Postings] struct {
+	p   []T
+	h   *loser.Tree[storage.SeriesRef, T]
 	cur storage.SeriesRef
 }
 
-func newMergedPostings(p []Postings) (m *mergedPostings, nonEmpty bool) {
+func newMergedPostings[T Postings](p []T) (m *mergedPostings[T], nonEmpty bool) {
 	const maxVal = storage.SeriesRef(math.MaxUint64) // This value must be higher than all real values used in the tree.
 	lt := loser.New(p, maxVal)
-	return &mergedPostings{p: p, h: lt}, true
+	return &mergedPostings[T]{p: p, h: lt}, true
 }
 
-func (it *mergedPostings) Next() bool {
+func (it *mergedPostings[T]) Next() bool {
 	for {
 		if !it.h.Next() {
 			return false
@@ -701,7 +701,7 @@ func (it *mergedPostings) Next() bool {
 	}
 }
 
-func (it *mergedPostings) Seek(id storage.SeriesRef) bool {
+func (it *mergedPostings[T]) Seek(id storage.SeriesRef) bool {
 	for !it.h.IsEmpty() && it.h.At() < id {
 		finished := !it.h.Winner().Seek(id)
 		it.h.Fix(finished)
@@ -713,11 +713,11 @@ func (it *mergedPostings) Seek(id storage.SeriesRef) bool {
 	return true
 }
 
-func (it mergedPostings) At() storage.SeriesRef {
+func (it mergedPostings[T]) At() storage.SeriesRef {
 	return it.cur
 }
 
-func (it mergedPostings) Err() error {
+func (it mergedPostings[T]) Err() error {
 	for _, p := range it.p {
 		if err := p.Err(); err != nil {
 			return err
diff --git a/tsdb/index/postings_test.go b/tsdb/index/postings_test.go
index cd7fa9d3c..77d59ec99 100644
--- a/tsdb/index/postings_test.go
+++ b/tsdb/index/postings_test.go
@@ -392,7 +392,7 @@ func BenchmarkMerge(t *testing.B) {
 		refs = append(refs, temp)
 	}
 
-	its := make([]Postings, len(refs))
+	its := make([]*ListPostings, len(refs))
 	for _, nSeries := range []int{1, 10, 10000, 100000} {
 		t.Run(strconv.Itoa(nSeries), func(bench *testing.B) {
 			ctx := context.Background()