diff --git a/tsdb/compact.go b/tsdb/compact.go
index acbdbf6443..1f172c8267 100644
--- a/tsdb/compact.go
+++ b/tsdb/compact.go
@@ -656,7 +656,9 @@ func (c *LeveledCompactor) populateBlock(blocks []BlockReader, meta *BlockMeta,
 	defer func() {
 		var merr tsdb_errors.MultiError
 		merr.Add(err)
-		merr.Add(closeAll(closers))
+		if cerr := closeAll(closers); cerr != nil {
+			merr.Add(errors.Wrap(err, "close"))
+		}
 		err = merr.Err()
 		c.metrics.populatingBlocks.Set(0)
 	}()
@@ -708,7 +710,6 @@ func (c *LeveledCompactor) populateBlock(blocks []BlockReader, meta *BlockMeta,
 
 		s := newCompactionSeriesSet(indexr, chunkr, tombsr, all)
 		syms := indexr.Symbols()
-
 		if i == 0 {
 			set = s
 			symbols = syms
diff --git a/tsdb/head.go b/tsdb/head.go
index 3b1d4ad057..7bef68a85e 100644
--- a/tsdb/head.go
+++ b/tsdb/head.go
@@ -46,6 +46,10 @@ var (
 	ErrInvalidSample = errors.New("invalid sample")
 )
 
+// TEST!
+var testSimulation1 sync.Mutex
+var testSimulation2 sync.Mutex
+
 // Head handles reads and writes of time series data within a time window.
 type Head struct {
 	// Keep all 64bit atomically accessed variables at the top of this struct.
@@ -1104,6 +1108,7 @@ func (a *headAppender) Add(lset labels.Labels, t int64, v float64) (uint64, erro
 	if err != nil {
 		return 0, err
 	}
+
 	if created {
 		a.series = append(a.series, record.RefSeries{
 			Ref:    s.ref,
@@ -1282,6 +1287,8 @@ func (h *Head) Delete(mint, maxt int64, ms ...*labels.Matcher) error {
 	return nil
 }
 
+var lockThings bool
+
 // gc removes data before the minimum timestamp from the head.
 func (h *Head) gc() {
 	// Only data strictly lower than this timestamp must be deleted.
@@ -1337,6 +1344,13 @@ func (h *Head) gc() {
 		panic(err)
 	}
 
+	if lockThings {
+		// Test purposes. Simulate runtime freezing this go routine and allowing append to continue.
+		testSimulation1.Unlock()
+		testSimulation2.Lock()
+		testSimulation2.Unlock()
+	}
+
 	h.symMtx.Lock()
 
 	h.symbols = symbols
@@ -1692,8 +1706,6 @@ func (h *Head) getOrCreateWithID(id, hash uint64, lset labels.Labels) (*memSerie
 	h.metrics.seriesCreated.Inc()
 	atomic.AddUint64(&h.numSeries, 1)
 
-	h.postings.Add(id, lset)
-
 	h.symMtx.Lock()
 	defer h.symMtx.Unlock()
 
@@ -1709,6 +1721,13 @@ func (h *Head) getOrCreateWithID(id, hash uint64, lset labels.Labels) (*memSerie
 		h.symbols[l.Value] = struct{}{}
 	}
 
+	h.postings.Add(id, lset)
+
+	if lockThings {
+		// Allow GC to continue and append wrong symbol with missing just added one! ):
+		testSimulation2.Unlock()
+	}
+
 	return s, true, nil
 }
 
diff --git a/tsdb/head_test.go b/tsdb/head_test.go
index 6c5e466587..22676dde80 100644
--- a/tsdb/head_test.go
+++ b/tsdb/head_test.go
@@ -1875,3 +1875,57 @@ func TestHeadLabelNamesValuesWithMinMaxRange(t *testing.T) {
 		})
 	}
 }
+
+// Regression test showing race between compact and append.
+func TestHeadCompactionRace(t *testing.T) {
+	db, closeFn := openTestDB(t, &Options{
+		RetentionDuration: 100000000,
+		NoLockfile:        true,
+		MinBlockDuration:  1000000,
+		MaxBlockDuration:  1000000,
+	}, []int64{1000000})
+	t.Cleanup(func() {
+		closeFn()
+		testutil.Ok(t, db.Close())
+	})
+
+	head := db.Head()
+
+	app := head.Appender()
+	_, err := app.Add(labels.Labels{labels.Label{Name: "n", Value: "v"}}, 10, 10)
+	testutil.Ok(t, err)
+	testutil.Ok(t, app.Commit())
+
+	var wg sync.WaitGroup
+
+	// Simulate racy gc vs append
+	testSimulation1.Lock()
+	testSimulation2.Lock()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+
+		testSimulation1.Lock()
+		testSimulation1.Unlock()
+		app := head.Appender()
+		_, err := app.Add(labels.Labels{labels.Label{Name: "n", Value: "v2"}}, 10, 10)
+		testutil.Ok(t, err)
+		testutil.Ok(t, app.Commit())
+	}()
+	lockThings = true
+	head.gc()
+	wg.Wait()
+
+	r, err := db.head.Index()
+	testutil.Ok(t, err)
+
+	all := r.Symbols()
+	var s []string
+	for all.Next() {
+		s = append(s, all.At())
+	}
+	testutil.Ok(t, all.Err())
+	testutil.Equals(t, []string{"", "n", "v2"}, s)
+
+}