diff --git a/CHANGELOG.md b/CHANGELOG.md
index f42a92474f..5f45847200 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,7 +1,6 @@
 ## master / unreleased
  - [CHANGE]  `NewLeveledCompactor` takes a context so that a compaction is canceled when closing the db.
  - [ENHANCEMENT] When closing the db any running compaction will be cancelled so it doesn't block.
-
  - [CHANGE] `prometheus_tsdb_storage_blocks_bytes_total` is now `prometheus_tsdb_storage_blocks_bytes`
 
 ## 0.4.0
diff --git a/compact.go b/compact.go
index 6702935c01..8a20dd1c64 100644
--- a/compact.go
+++ b/compact.go
@@ -82,7 +82,7 @@ type LeveledCompactor struct {
 
 type compactorMetrics struct {
 	ran              prometheus.Counter
-	populatingBlocks prometheus.Counter
+	populatingBlocks prometheus.Gauge
 	failed           prometheus.Counter
 	duration         prometheus.Histogram
 	chunkSize        prometheus.Histogram
@@ -486,12 +486,12 @@ func (w *instrumentedChunkWriter) WriteChunks(chunks ...chunks.Meta) error {
 func (c *LeveledCompactor) write(dest string, meta *BlockMeta, blocks ...BlockReader) (err error) {
 	dir := filepath.Join(dest, meta.ULID.String())
 	tmp := dir + ".tmp"
-	var writers []io.Closer
+	var closers []io.Closer
 	defer func(t time.Time) {
 		var merr MultiError
 		merr.Add(err)
 		err = merr.Err()
-		for _, w := range writers {
+		for _, w := range closers {
 			merr.Add(w.Close())
 		}
 
@@ -522,7 +522,7 @@ func (c *LeveledCompactor) write(dest string, meta *BlockMeta, blocks ...BlockRe
 	if err != nil {
 		return errors.Wrap(err, "open chunk writer")
 	}
-	writers = append(writers, chunkw)
+	closers = append(closers, chunkw)
 	// Record written chunk sizes on level 1 compactions.
 	if meta.Compaction.Level == 1 {
 		chunkw = &instrumentedChunkWriter{
@@ -537,7 +537,7 @@ func (c *LeveledCompactor) write(dest string, meta *BlockMeta, blocks ...BlockRe
 	if err != nil {
 		return errors.Wrap(err, "open index writer")
 	}
-	writers = append(writers, indexw)
+	closers = append(closers, indexw)
 
 	if err := c.populateBlock(blocks, meta, indexw, chunkw); err != nil {
 		return errors.Wrap(err, "write compaction")
@@ -554,10 +554,10 @@ func (c *LeveledCompactor) write(dest string, meta *BlockMeta, blocks ...BlockRe
 	// you cannot delete these unless they are closed and the defer is to
 	// make sure they are closed if the function exits due to an error above.
 	var merr MultiError
-	for _, w := range writers {
+	for _, w := range closers {
 		merr.Add(w.Close())
 	}
-	writers = writers[:0] // Avoid closing the writers twice in the defer.
+	closers = closers[:0] // Avoid closing the writers twice in the defer.
 	if merr.Err() != nil {
 		return merr.Err()
 	}
@@ -618,10 +618,10 @@ func (c *LeveledCompactor) populateBlock(blocks []BlockReader, meta *BlockMeta,
 	)
 	defer func() {
 		closeAll(closers...)
-		c.metrics.populatingBlocks.Add(-1)
+		c.metrics.populatingBlocks.Set(0)
 	}()
 
-	c.metrics.populatingBlocks.Inc()
+	c.metrics.populatingBlocks.Set(1)
 
 	for i, b := range blocks {
 		select {