diff --git a/promql/analyzer.go b/promql/analyzer.go
index 7243d31db..a3319b211 100644
--- a/promql/analyzer.go
+++ b/promql/analyzer.go
@@ -27,7 +27,7 @@ import (
 // from the storage. It is bound to a context that allows cancellation and timing out.
 type Analyzer struct {
 	// The storage from which to query data.
-	Storage local.Storage
+	Storage local.Querier
 	// The expression being analyzed.
 	Expr Expr
 	// The time range for evaluation of Expr.
diff --git a/promql/engine.go b/promql/engine.go
index 23dfeef25..8a7ad6d66 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -218,7 +218,7 @@ func contextDone(ctx context.Context, env string) error {
 // It is connected to a storage.
 type Engine struct {
 	// The storage on which the engine operates.
-	storage local.Storage
+	storage local.Querier
 
 	// The base context for all queries and its cancellation function.
 	baseCtx       context.Context
@@ -230,7 +230,7 @@ type Engine struct {
 }
 
 // NewEngine returns a new engine.
-func NewEngine(storage local.Storage, o *EngineOptions) *Engine {
+func NewEngine(storage local.Querier, o *EngineOptions) *Engine {
 	if o == nil {
 		o = DefaultEngineOptions
 	}
diff --git a/storage/local/interface.go b/storage/local/interface.go
index 26bc5325a..be9b31bab 100644
--- a/storage/local/interface.go
+++ b/storage/local/interface.go
@@ -16,27 +16,45 @@ package local
 import (
 	"time"
 
-	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
 
+	"github.com/prometheus/prometheus/storage"
 	"github.com/prometheus/prometheus/storage/metric"
 )
 
 // Storage ingests and manages samples, along with various indexes. All methods
 // are goroutine-safe. Storage implements storage.SampleAppender.
 type Storage interface {
-	prometheus.Collector
-	// Append stores a sample in the Storage. Multiple samples for the same
-	// fingerprint need to be submitted in chronological order, from oldest
-	// to newest. When Append has returned, the appended sample might not be
-	// queryable immediately. (Use WaitForIndexing to wait for complete
-	// processing.) The implementation might remove labels with empty value
-	// from the provided Sample as those labels are considered equivalent to
-	// a label not present at all.
-	Append(*model.Sample) error
-	// NeedsThrottling returns true if the Storage has too many chunks in memory
+	Querier
+
+	// This SampleAppender needs multiple samples for the same fingerprint to be
+	// submitted in chronological order, from oldest to newest. When Append has
+	// returned, the appended sample might not be queryable immediately. (Use
+	// WaitForIndexing to wait for complete processing.) The implementation might
+	// remove labels with empty value from the provided Sample as those labels
+	// are considered equivalent to a label not present at all.
+	//
+	// Appending is throttled if the Storage has too many chunks in memory
 	// already or has too many chunks waiting for persistence.
-	NeedsThrottling() bool
+	storage.SampleAppender
+
+	// Drop all time series associated with the given fingerprints.
+	DropMetricsForFingerprints(...model.Fingerprint)
+	// Run the various maintenance loops in goroutines. Returns when the
+	// storage is ready to use. Keeps everything running in the background
+	// until Stop is called.
+	Start() error
+	// Stop shuts down the Storage gracefully, flushes all pending
+	// operations, stops all maintenance loops,and frees all resources.
+	Stop() error
+	// WaitForIndexing returns once all samples in the storage are
+	// indexed. Indexing is needed for FingerprintsForLabelMatchers and
+	// LabelValuesForLabelName and may lag behind.
+	WaitForIndexing()
+}
+
+// Querier allows querying a time series storage.
+type Querier interface {
 	// NewPreloader returns a new Preloader which allows preloading and pinning
 	// series data into memory for use within a query.
 	NewPreloader() Preloader
@@ -56,19 +74,6 @@ type Storage interface {
 	LastSampleForFingerprint(model.Fingerprint) model.Sample
 	// Get all of the label values that are associated with a given label name.
 	LabelValuesForLabelName(model.LabelName) model.LabelValues
-	// Drop all time series associated with the given fingerprints.
-	DropMetricsForFingerprints(...model.Fingerprint)
-	// Run the various maintenance loops in goroutines. Returns when the
-	// storage is ready to use. Keeps everything running in the background
-	// until Stop is called.
-	Start() error
-	// Stop shuts down the Storage gracefully, flushes all pending
-	// operations, stops all maintenance loops,and frees all resources.
-	Stop() error
-	// WaitForIndexing returns once all samples in the storage are
-	// indexed. Indexing is needed for FingerprintsForLabelMatchers and
-	// LabelValuesForLabelName and may lag behind.
-	WaitForIndexing()
 }
 
 // SeriesIterator enables efficient access of sample values in a series. Its
diff --git a/storage/local/storage.go b/storage/local/storage.go
index fb97dd603..9a817e381 100644
--- a/storage/local/storage.go
+++ b/storage/local/storage.go
@@ -189,7 +189,7 @@ type MemorySeriesStorageOptions struct {
 
 // NewMemorySeriesStorage returns a newly allocated Storage. Storage.Serve still
 // has to be called to start the storage.
-func NewMemorySeriesStorage(o *MemorySeriesStorageOptions) Storage {
+func NewMemorySeriesStorage(o *MemorySeriesStorageOptions) *memorySeriesStorage {
 	s := &memorySeriesStorage{
 		fpLocker: newFingerprintLocker(o.NumMutexes),
 
diff --git a/storage/local/storage_test.go b/storage/local/storage_test.go
index 476fe60c8..48eb34184 100644
--- a/storage/local/storage_test.go
+++ b/storage/local/storage_test.go
@@ -718,7 +718,7 @@ func TestLoop(t *testing.T) {
 		storage.Append(s)
 	}
 	storage.WaitForIndexing()
-	series, _ := storage.(*memorySeriesStorage).fpToSeries.get(model.Metric{}.FastFingerprint())
+	series, _ := storage.fpToSeries.get(model.Metric{}.FastFingerprint())
 	cdsBefore := len(series.chunkDescs)
 	time.Sleep(fpMaxWaitDuration + time.Second) // TODO(beorn7): Ugh, need to wait for maintenance to kick in.
 	cdsAfter := len(series.chunkDescs)
@@ -1497,12 +1497,12 @@ func benchmarkFuzz(b *testing.B, encoding chunkEncoding) {
 		for _, sample := range samples[start:middle] {
 			s.Append(sample)
 		}
-		verifyStorageRandom(b, s.(*memorySeriesStorage), samples[:middle])
+		verifyStorageRandom(b, s, samples[:middle])
 		for _, sample := range samples[middle:end] {
 			s.Append(sample)
 		}
-		verifyStorageRandom(b, s.(*memorySeriesStorage), samples[:end])
-		verifyStorageSequential(b, s.(*memorySeriesStorage), samples)
+		verifyStorageRandom(b, s, samples[:end])
+		verifyStorageSequential(b, s, samples)
 	}
 }
 
diff --git a/storage/local/test_helpers.go b/storage/local/test_helpers.go
index 1dedf518e..3695ea310 100644
--- a/storage/local/test_helpers.go
+++ b/storage/local/test_helpers.go
@@ -52,7 +52,7 @@ func NewTestStorage(t testutil.T, encoding chunkEncoding) (*memorySeriesStorage,
 		SyncStrategy:               Adaptive,
 	}
 	storage := NewMemorySeriesStorage(o)
-	storage.(*memorySeriesStorage).archiveHighWatermark = model.Latest
+	storage.archiveHighWatermark = model.Latest
 	if err := storage.Start(); err != nil {
 		directory.Close()
 		t.Fatalf("Error creating storage: %s", err)
@@ -63,5 +63,5 @@ func NewTestStorage(t testutil.T, encoding chunkEncoding) (*memorySeriesStorage,
 		directory: directory,
 	}
 
-	return storage.(*memorySeriesStorage), closer
+	return storage, closer
 }