diff --git a/tsdb/compact.go b/tsdb/compact.go
index 7c12d1729..1d7e93f7f 100644
--- a/tsdb/compact.go
+++ b/tsdb/compact.go
@@ -18,7 +18,6 @@ import (
 	"crypto/rand"
 	"fmt"
 	"io"
-	"math"
 	"os"
 	"path/filepath"
 	"sort"
@@ -347,19 +346,20 @@ func splitByRange(ds []dirMeta, tr int64) [][]dirMeta {
 }
 
 // CompactBlockMetas merges many block metas into one, combining it's source blocks together
-// and adjusting compaction level.
+// and adjusting compaction level. Min/Max time of result block meta covers all input blocks.
 func CompactBlockMetas(uid ulid.ULID, blocks ...*BlockMeta) *BlockMeta {
 	res := &BlockMeta{
-		ULID:    uid,
-		MinTime: blocks[0].MinTime,
+		ULID: uid,
 	}
 
 	sources := map[ulid.ULID]struct{}{}
-	// For overlapping blocks, the Maxt can be
-	// in any block so we track it globally.
-	maxt := int64(math.MinInt64)
+	mint := blocks[0].MinTime
+	maxt := blocks[0].MaxTime
 
 	for _, b := range blocks {
+		if b.MinTime < mint {
+			mint = b.MinTime
+		}
 		if b.MaxTime > maxt {
 			maxt = b.MaxTime
 		}
@@ -384,6 +384,7 @@ func CompactBlockMetas(uid ulid.ULID, blocks ...*BlockMeta) *BlockMeta {
 		return res.Compaction.Sources[i].Compare(res.Compaction.Sources[j]) < 0
 	})
 
+	res.MinTime = mint
 	res.MaxTime = maxt
 	return res
 }
diff --git a/tsdb/compact_test.go b/tsdb/compact_test.go
index bac9bfdfe..dc8ffc85f 100644
--- a/tsdb/compact_test.go
+++ b/tsdb/compact_test.go
@@ -25,6 +25,7 @@ import (
 	"time"
 
 	"github.com/go-kit/log"
+	"github.com/oklog/ulid"
 	"github.com/pkg/errors"
 	prom_testutil "github.com/prometheus/client_golang/prometheus/testutil"
 	"github.com/stretchr/testify/require"
@@ -1311,3 +1312,38 @@ func TestDeleteCompactionBlockAfterFailedReload(t *testing.T) {
 		})
 	}
 }
+
+func TestCompactBlockMetas(t *testing.T) {
+	parent1 := ulid.MustNew(100, nil)
+	parent2 := ulid.MustNew(200, nil)
+	parent3 := ulid.MustNew(300, nil)
+	parent4 := ulid.MustNew(400, nil)
+
+	input := []*BlockMeta{
+		{ULID: parent1, MinTime: 1000, MaxTime: 2000, Compaction: BlockMetaCompaction{Level: 2, Sources: []ulid.ULID{ulid.MustNew(1, nil), ulid.MustNew(10, nil)}}},
+		{ULID: parent2, MinTime: 200, MaxTime: 500, Compaction: BlockMetaCompaction{Level: 1}},
+		{ULID: parent3, MinTime: 500, MaxTime: 2500, Compaction: BlockMetaCompaction{Level: 3, Sources: []ulid.ULID{ulid.MustNew(5, nil), ulid.MustNew(6, nil)}}},
+		{ULID: parent4, MinTime: 100, MaxTime: 900, Compaction: BlockMetaCompaction{Level: 1}},
+	}
+
+	outUlid := ulid.MustNew(1000, nil)
+	output := CompactBlockMetas(outUlid, input...)
+
+	expected := &BlockMeta{
+		ULID:    outUlid,
+		MinTime: 100,
+		MaxTime: 2500,
+		Stats:   BlockStats{},
+		Compaction: BlockMetaCompaction{
+			Level:   4,
+			Sources: []ulid.ULID{ulid.MustNew(1, nil), ulid.MustNew(5, nil), ulid.MustNew(6, nil), ulid.MustNew(10, nil)},
+			Parents: []BlockDesc{
+				{ULID: parent1, MinTime: 1000, MaxTime: 2000},
+				{ULID: parent2, MinTime: 200, MaxTime: 500},
+				{ULID: parent3, MinTime: 500, MaxTime: 2500},
+				{ULID: parent4, MinTime: 100, MaxTime: 900},
+			},
+		},
+	}
+	require.Equal(t, expected, output)
+}