diff --git a/storage/merge.go b/storage/merge.go
index 61f873cf36..e1c248cb46 100644
--- a/storage/merge.go
+++ b/storage/merge.go
@@ -693,7 +693,7 @@ func estimateCompactedChunkCount(series []ChunkSeries) int {
 	for _, s := range series {
 		iter := s.Iterator(nil)
 		if iter.Next() {
-			h.Push(iter)
+			heap.Push(&h, iter)
 		}
 	}
 
diff --git a/storage/merge_test.go b/storage/merge_test.go
index 98daed10c5..e5eb296d1b 100644
--- a/storage/merge_test.go
+++ b/storage/merge_test.go
@@ -429,6 +429,14 @@ func TestCompactingChunkSeriesMerger(t *testing.T) {
 			},
 			expected: NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{fSample{1, 1}, fSample{2, 2}}, []tsdbutil.Sample{fSample{3, 3}, fSample{5, 5}}, []tsdbutil.Sample{fSample{7, 7}, fSample{9, 9}}, []tsdbutil.Sample{fSample{10, 10}}),
 		},
+		{
+			name: "two non overlapping in reverse order",
+			input: []ChunkSeries{
+				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{fSample{7, 7}, fSample{9, 9}}, []tsdbutil.Sample{fSample{10, 10}}),
+				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{fSample{1, 1}, fSample{2, 2}}, []tsdbutil.Sample{fSample{3, 3}, fSample{5, 5}}),
+			},
+			expected: NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{fSample{1, 1}, fSample{2, 2}}, []tsdbutil.Sample{fSample{3, 3}, fSample{5, 5}}, []tsdbutil.Sample{fSample{7, 7}, fSample{9, 9}}, []tsdbutil.Sample{fSample{10, 10}}),
+		},
 		{
 			name: "two overlapping",
 			input: []ChunkSeries{