diff --git a/storage/fanout.go b/storage/fanout.go
index 061d993af..ae74ad2ca 100644
--- a/storage/fanout.go
+++ b/storage/fanout.go
@@ -225,7 +225,7 @@ func (q *mergeQuerier) Select(matchers ...*labels.Matcher) (SeriesSet, error) {
 		}
 		seriesSets = append(seriesSets, set)
 	}
-	return newMergeSeriesSet(seriesSets), nil
+	return NewMergeSeriesSet(seriesSets), nil
 }
 
 // LabelValues returns all potential values for a label name.
@@ -300,7 +300,9 @@ type mergeSeriesSet struct {
 	sets          []SeriesSet
 }
 
-func newMergeSeriesSet(sets []SeriesSet) SeriesSet {
+// NewMergeSeriesSet returns a new series set that merges (deduplicates)
+// series returned by the input series sets when iterating.
+func NewMergeSeriesSet(sets []SeriesSet) SeriesSet {
 	// Sets need to be pre-advanced, so we can introspect the label of the
 	// series under the cursor.
 	var h seriesSetHeap
diff --git a/storage/fanout_test.go b/storage/fanout_test.go
index d8354b442..c8094ea33 100644
--- a/storage/fanout_test.go
+++ b/storage/fanout_test.go
@@ -97,7 +97,7 @@ func TestMergeSeriesSet(t *testing.T) {
 			),
 		},
 	} {
-		merged := newMergeSeriesSet(tc.input)
+		merged := NewMergeSeriesSet(tc.input)
 		for merged.Next() {
 			require.True(t, tc.expected.Next())
 			actualSeries := merged.At()
diff --git a/storage/interface.go b/storage/interface.go
index 71261b2c9..e04126cc9 100644
--- a/storage/interface.go
+++ b/storage/interface.go
@@ -110,73 +110,3 @@ type SeriesIterator interface {
 	// Err returns the current error.
 	Err() error
 }
-
-// dedupedSeriesSet takes two series sets and returns them deduplicated.
-// The input sets must be sorted and identical if two series exist in both, i.e.
-// if their label sets are equal, the datapoints must be equal as well.
-type dedupedSeriesSet struct {
-	a, b SeriesSet
-
-	cur          Series
-	adone, bdone bool
-}
-
-// DeduplicateSeriesSet merges two SeriesSet and removes duplicates.
-// If two series exist in both sets, their datapoints must be equal.
-func DeduplicateSeriesSet(a, b SeriesSet) SeriesSet {
-	if a == nil {
-		return b
-	}
-	if b == nil {
-		return a
-	}
-
-	s := &dedupedSeriesSet{a: a, b: b}
-	s.adone = !s.a.Next()
-	s.bdone = !s.b.Next()
-
-	return s
-}
-
-func (s *dedupedSeriesSet) At() Series {
-	return s.cur
-}
-
-func (s *dedupedSeriesSet) Err() error {
-	if s.a.Err() != nil {
-		return s.a.Err()
-	}
-	return s.b.Err()
-}
-
-func (s *dedupedSeriesSet) compare() int {
-	if s.adone {
-		return 1
-	}
-	if s.bdone {
-		return -1
-	}
-	return labels.Compare(s.a.At().Labels(), s.b.At().Labels())
-}
-
-func (s *dedupedSeriesSet) Next() bool {
-	if s.adone && s.bdone || s.Err() != nil {
-		return false
-	}
-
-	d := s.compare()
-
-	// Both sets contain the current series. Chain them into a single one.
-	if d > 0 {
-		s.cur = s.b.At()
-		s.bdone = !s.b.Next()
-	} else if d < 0 {
-		s.cur = s.a.At()
-		s.adone = !s.a.Next()
-	} else {
-		s.cur = s.a.At()
-		s.adone = !s.a.Next()
-		s.bdone = !s.b.Next()
-	}
-	return true
-}
diff --git a/web/api/v1/api.go b/web/api/v1/api.go
index 56d0d37ed..257ebcd29 100644
--- a/web/api/v1/api.go
+++ b/web/api/v1/api.go
@@ -394,18 +394,17 @@ func (api *API) series(r *http.Request) (interface{}, *apiError) {
 	}
 	defer q.Close()
 
-	var set storage.SeriesSet
-
+	var sets []storage.SeriesSet
 	for _, mset := range matcherSets {
 		s, err := q.Select(mset...)
 		if err != nil {
 			return nil, &apiError{errorExec, err}
 		}
-		set = storage.DeduplicateSeriesSet(set, s)
+		sets = append(sets, s)
 	}
 
+	set := storage.NewMergeSeriesSet(sets)
 	metrics := []labels.Labels{}
-
 	for set.Next() {
 		metrics = append(metrics, set.At().Labels())
 	}
diff --git a/web/federate.go b/web/federate.go
index 43028a3ac..8640a886d 100644
--- a/web/federate.go
+++ b/web/federate.go
@@ -72,8 +72,7 @@ func (h *Handler) federation(w http.ResponseWriter, req *http.Request) {
 
 	vec := make(promql.Vector, 0, 8000)
 
-	var set storage.SeriesSet
-
+	var sets []storage.SeriesSet
 	for _, mset := range matcherSets {
 		s, err := q.Select(mset...)
 		if err != nil {
@@ -81,12 +80,10 @@ func (h *Handler) federation(w http.ResponseWriter, req *http.Request) {
 			http.Error(w, err.Error(), http.StatusInternalServerError)
 			return
 		}
-		set = storage.DeduplicateSeriesSet(set, s)
-	}
-	if set == nil {
-		return
+		sets = append(sets, s)
 	}
 
+	set := storage.NewMergeSeriesSet(sets)
 	for set.Next() {
 		s := set.At()