diff --git a/tsdb/engine/tsm1/file_store.go b/tsdb/engine/tsm1/file_store.go
index 6d53020340..ccc0866839 100644
--- a/tsdb/engine/tsm1/file_store.go
+++ b/tsdb/engine/tsm1/file_store.go
@@ -635,35 +635,26 @@ func (f *FileStore) walkFiles(fn func(f TSMFile) error) error {
 	defer f.mu.RUnlock()
 
 	// struct to hold the result of opening each reader in a goroutine
-	type res struct {
-		err error
-	}
-
-	resC := make(chan res)
-	var n int
 
+	errC := make(chan error, len(f.files))
 	for _, f := range f.files {
-		n++
-
 		go func(tsm TSMFile) {
 			if err := fn(tsm); err != nil {
-				resC <- res{err: fmt.Errorf("file %s: %s", tsm.Path(), err)}
+				errC <- fmt.Errorf("file %s: %s", tsm.Path(), err)
 				return
 			}
 
-			resC <- res{}
+			errC <- nil
 		}(f)
 	}
 
-	var err error
-	for i := 0; i < n; i++ {
-		res := <-resC
-		if res.err != nil {
-			err = res.err
+	for i := 0; i < cap(errC); i++ {
+		res := <-errC
+		if res != nil {
+			return res
 		}
 	}
-	close(resC)
-	return err
+	return nil
 }
 
 // locations returns the files and index blocks for a key and time.  ascending indicates
diff --git a/tsdb/engine/tsm1/reader.go b/tsdb/engine/tsm1/reader.go
index 6ef995b568..3534223c4d 100644
--- a/tsdb/engine/tsm1/reader.go
+++ b/tsdb/engine/tsm1/reader.go
@@ -215,7 +215,7 @@ func (t *TSMReader) applyTombstones() error {
 		}
 		batch = append(batch, ts.Key)
 
-		if len(batch) > 4096 {
+		if len(batch) >= 4096 {
 			t.index.DeleteRange(batch, prev.Min, prev.Max)
 			batch = batch[:0]
 		}
diff --git a/tsdb/engine/tsm1/tombstone.go b/tsdb/engine/tsm1/tombstone.go
index 3e67333d97..1619af0e8a 100644
--- a/tsdb/engine/tsm1/tombstone.go
+++ b/tsdb/engine/tsm1/tombstone.go
@@ -11,7 +11,10 @@ import (
 	"sync"
 )
 
-const v2header = 0x1502
+const (
+	v2header     = 0x1502
+	v2headerSize = 4
+)
 
 type Tombstoner struct {
 	mu sync.Mutex
@@ -116,8 +119,7 @@ func (t *Tombstoner) Walk(fn func(t Tombstone) error) error {
 	defer f.Close()
 
 	var b [4]byte
-	_, err = f.Read(b[:])
-	if err != nil {
+	if _, err := f.Read(b[:]); err != nil {
 		// Might be a zero length file which should not exist, but
 		// an old bug allowed them to occur.  Treat it as an empty
 		// v1 tombstone file so we don't abort loading the TSM file.
@@ -221,7 +223,7 @@ func (t *Tombstoner) readTombstoneV1(f *os.File, fn func(t Tombstone) error) err
 // format is binary.
 func (t *Tombstoner) readTombstoneV2(f *os.File, fn func(t Tombstone) error) error {
 	// Skip header, already checked earlier
-	if _, err := f.Seek(4, os.SEEK_SET); err != nil {
+	if _, err := f.Seek(v2headerSize, os.SEEK_SET); err != nil {
 		return err
 	}
 	n := int64(4)