diff --git a/compact.go b/compact.go
index 37fa3ae00..556856107 100644
--- a/compact.go
+++ b/compact.go
@@ -76,12 +76,13 @@ type LeveledCompactor struct {
 }
 
 type compactorMetrics struct {
-	ran          prometheus.Counter
-	failed       prometheus.Counter
-	duration     prometheus.Histogram
-	chunkSize    prometheus.Histogram
-	chunkSamples prometheus.Histogram
-	chunkRange   prometheus.Histogram
+	ran              prometheus.Counter
+	populatingBlocks prometheus.Counter
+	failed           prometheus.Counter
+	duration         prometheus.Histogram
+	chunkSize        prometheus.Histogram
+	chunkSamples     prometheus.Histogram
+	chunkRange       prometheus.Histogram
 }
 
 func newCompactorMetrics(r prometheus.Registerer) *compactorMetrics {
@@ -91,6 +92,10 @@ func newCompactorMetrics(r prometheus.Registerer) *compactorMetrics {
 		Name: "prometheus_tsdb_compactions_total",
 		Help: "Total number of compactions that were executed for the partition.",
 	})
+	m.populatingBlocks = prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "prometheus_tsdb_compaction_populating_block",
+		Help: "Set to 1 when a block is currently being written to the disk.",
+	})
 	m.failed = prometheus.NewCounter(prometheus.CounterOpts{
 		Name: "prometheus_tsdb_compactions_failed_total",
 		Help: "Total number of compactions that failed for the partition.",
@@ -119,6 +124,7 @@ func newCompactorMetrics(r prometheus.Registerer) *compactorMetrics {
 	if r != nil {
 		r.MustRegister(
 			m.ran,
+			m.populatingBlocks,
 			m.failed,
 			m.duration,
 			m.chunkRange,
@@ -569,8 +575,12 @@ func (c *LeveledCompactor) populateBlock(blocks []BlockReader, meta *BlockMeta,
 		allSymbols = make(map[string]struct{}, 1<<16)
 		closers    = []io.Closer{}
 	)
-	defer func() { closeAll(closers...) }()
+	defer func() {
+		closeAll(closers...)
+		c.metrics.populatingBlocks.Add(-1)
+	}()
 
+	c.metrics.populatingBlocks.Inc()
 	for i, b := range blocks {
 		select {
 		case <-c.ctx.Done():
diff --git a/compact_test.go b/compact_test.go
index 89c36767f..36bcb220c 100644
--- a/compact_test.go
+++ b/compact_test.go
@@ -24,6 +24,7 @@ import (
 
 	"github.com/go-kit/kit/log"
 	"github.com/pkg/errors"
+	prom_testutil "github.com/prometheus/client_golang/prometheus/testutil"
 	dto "github.com/prometheus/client_model/go"
 	"github.com/prometheus/tsdb/chunks"
 	"github.com/prometheus/tsdb/labels"
@@ -742,3 +743,38 @@ func TestDisableAutoCompactions(t *testing.T) {
 	}
 	testutil.Assert(t, len(db.Blocks()) > 0, "No block was persisted after the set timeout.")
 }
+
+// TestCancelCompactions ensures that when the db is closed
+// any running compaction is cancelled to unblock closing the db.
+func TestCancelCompactions(t *testing.T) {
+	tmpdir, err := ioutil.TempDir("", "test")
+	testutil.Ok(t, err)
+	defer os.RemoveAll(tmpdir)
+
+	// Create some blocks to fall within the compaction range.
+	createPopulatedBlock(t, tmpdir, 3000, 0, 1000)
+	createPopulatedBlock(t, tmpdir, 3000, 1000, 2000)
+	createPopulatedBlock(t, tmpdir, 1, 2000, 2001)
+
+	db, err := Open(tmpdir, log.NewNopLogger(), nil, &Options{BlockRanges: []int64{1, 2000}})
+	testutil.Ok(t, err)
+
+	db.compactc <- struct{}{} // Trigger a compaction.
+	dbClosed := make(chan struct{})
+	for {
+		if prom_testutil.ToFloat64(db.compactor.(*LeveledCompactor).metrics.populatingBlocks) > 0 {
+			time.Sleep(5 * time.Millisecond)
+			go func() {
+				testutil.Ok(t, db.Close())
+				close(dbClosed)
+			}()
+			break
+		}
+	}
+
+	start := time.Now()
+	<-dbClosed
+	actT := time.Since(start)
+	expT := time.Duration(50000000)
+	testutil.Assert(t, actT < expT, "closing the db took more than expected. exp: <%v, act: %v", expT, actT)
+}