diff --git a/storage/local/delta.go b/storage/local/delta.go
index 4d481aa77..9ea35f004 100644
--- a/storage/local/delta.go
+++ b/storage/local/delta.go
@@ -108,7 +108,7 @@ func (c deltaEncodedChunk) baseValue() clientmodel.SampleValue {
 
 // add implements chunk.
 func (c deltaEncodedChunk) add(s *metric.SamplePair) []chunk {
-	if len(c) < deltaHeaderBytes {
+	if c.len() == 0 {
 		c = c[:deltaHeaderBytes]
 		binary.LittleEndian.PutUint64(c[deltaHeaderBaseTimeOffset:], uint64(s.Timestamp))
 		binary.LittleEndian.PutUint64(c[deltaHeaderBaseValueOffset:], math.Float64bits(float64(s.Value)))
diff --git a/storage/local/doubledelta.go b/storage/local/doubledelta.go
index 58fd98955..bc8abdd0d 100644
--- a/storage/local/doubledelta.go
+++ b/storage/local/doubledelta.go
@@ -150,71 +150,15 @@ func (c doubleDeltaEncodedChunk) isInt() bool {
 
 // add implements chunk.
 func (c doubleDeltaEncodedChunk) add(s *metric.SamplePair) []chunk {
-	if len(c) <= doubleDeltaHeaderIsIntOffset+1 {
-		// This is the first sample added to this chunk. Add it as base
-		// time and value.
-		c = c[:doubleDeltaHeaderBaseValueOffset+8]
-		binary.LittleEndian.PutUint64(
-			c[doubleDeltaHeaderBaseTimeOffset:],
-			uint64(s.Timestamp),
-		)
-		binary.LittleEndian.PutUint64(
-			c[doubleDeltaHeaderBaseValueOffset:],
-			math.Float64bits(float64(s.Value)),
-		)
-		return []chunk{&c}
+	if c.len() == 0 {
+		return c.addFirstSample(s)
 	}
 
 	tb := c.timeBytes()
 	vb := c.valueBytes()
 
-	if len(c) <= doubleDeltaHeaderBaseValueOffset+8 {
-		// This is the 2nd sample added to this chunk. Calculate the
-		// base deltas.
-		baseTimeDelta := s.Timestamp - c.baseTime()
-		if baseTimeDelta < 0 {
-			// TODO(beorn7): We ignore this irregular case for now. Once
-			// https://github.com/prometheus/prometheus/issues/481 is
-			// fixed, we should panic here instead.
-			return []chunk{&c}
-		}
-		c = c[:doubleDeltaHeaderBytes]
-		if tb >= d8 || bytesNeededForUnsignedTimestampDelta(baseTimeDelta) >= d8 {
-			// If already the base delta needs d8 (or we are at d8
-			// already, anyway), we better encode this timestamp
-			// directly rather than as a delta and switch everything
-			// to d8.
-			c[doubleDeltaHeaderTimeBytesOffset] = byte(d8)
-			binary.LittleEndian.PutUint64(
-				c[doubleDeltaHeaderBaseTimeDeltaOffset:],
-				uint64(s.Timestamp),
-			)
-		} else {
-			binary.LittleEndian.PutUint64(
-				c[doubleDeltaHeaderBaseTimeDeltaOffset:],
-				uint64(baseTimeDelta),
-			)
-		}
-		baseValue := c.baseValue()
-		baseValueDelta := s.Value - baseValue
-		if vb >= d8 || baseValue+baseValueDelta != s.Value {
-			// If we can't reproduce the original sample value (or
-			// if we are at d8 already, anyway), we better encode
-			// this value directly rather than as a delta and switch
-			// everything to d8.
-			c[doubleDeltaHeaderValueBytesOffset] = byte(d8)
-			c[doubleDeltaHeaderIsIntOffset] = 0
-			binary.LittleEndian.PutUint64(
-				c[doubleDeltaHeaderBaseValueDeltaOffset:],
-				math.Float64bits(float64(s.Value)),
-			)
-		} else {
-			binary.LittleEndian.PutUint64(
-				c[doubleDeltaHeaderBaseValueDeltaOffset:],
-				math.Float64bits(float64(baseValueDelta)),
-			)
-		}
-		return []chunk{&c}
+	if c.len() == 1 {
+		return c.addSecondSample(s, tb, vb)
 	}
 
 	remainingBytes := cap(c) - len(c)
@@ -298,6 +242,70 @@ func (c doubleDeltaEncodedChunk) add(s *metric.SamplePair) []chunk {
 	return []chunk{&c}
 }
 
+// addFirstSample is a helper method only used by c.add(). It adds timestamp and
+// value as base time and value.
+func (c doubleDeltaEncodedChunk) addFirstSample(s *metric.SamplePair) []chunk {
+	c = c[:doubleDeltaHeaderBaseValueOffset+8]
+	binary.LittleEndian.PutUint64(
+		c[doubleDeltaHeaderBaseTimeOffset:],
+		uint64(s.Timestamp),
+	)
+	binary.LittleEndian.PutUint64(
+		c[doubleDeltaHeaderBaseValueOffset:],
+		math.Float64bits(float64(s.Value)),
+	)
+	return []chunk{&c}
+}
+
+// addSecondSample is a helper method only used by c.add(). It calculates the
+// base delta from the provided sample and adds it to the chunk.
+func (c doubleDeltaEncodedChunk) addSecondSample(s *metric.SamplePair, tb, vb deltaBytes) []chunk {
+	baseTimeDelta := s.Timestamp - c.baseTime()
+	if baseTimeDelta < 0 {
+		// TODO(beorn7): We ignore this irregular case for now. Once
+		// https://github.com/prometheus/prometheus/issues/481 is
+		// fixed, we should panic here instead.
+		return []chunk{&c}
+	}
+	c = c[:doubleDeltaHeaderBytes]
+	if tb >= d8 || bytesNeededForUnsignedTimestampDelta(baseTimeDelta) >= d8 {
+		// If already the base delta needs d8 (or we are at d8
+		// already, anyway), we better encode this timestamp
+		// directly rather than as a delta and switch everything
+		// to d8.
+		c[doubleDeltaHeaderTimeBytesOffset] = byte(d8)
+		binary.LittleEndian.PutUint64(
+			c[doubleDeltaHeaderBaseTimeDeltaOffset:],
+			uint64(s.Timestamp),
+		)
+	} else {
+		binary.LittleEndian.PutUint64(
+			c[doubleDeltaHeaderBaseTimeDeltaOffset:],
+			uint64(baseTimeDelta),
+		)
+	}
+	baseValue := c.baseValue()
+	baseValueDelta := s.Value - baseValue
+	if vb >= d8 || baseValue+baseValueDelta != s.Value {
+		// If we can't reproduce the original sample value (or
+		// if we are at d8 already, anyway), we better encode
+		// this value directly rather than as a delta and switch
+		// everything to d8.
+		c[doubleDeltaHeaderValueBytesOffset] = byte(d8)
+		c[doubleDeltaHeaderIsIntOffset] = 0
+		binary.LittleEndian.PutUint64(
+			c[doubleDeltaHeaderBaseValueDeltaOffset:],
+			math.Float64bits(float64(s.Value)),
+		)
+	} else {
+		binary.LittleEndian.PutUint64(
+			c[doubleDeltaHeaderBaseValueDeltaOffset:],
+			math.Float64bits(float64(baseValueDelta)),
+		)
+	}
+	return []chunk{&c}
+}
+
 // clone implements chunk.
 func (c doubleDeltaEncodedChunk) clone() chunk {
 	clone := make(doubleDeltaEncodedChunk, len(c), cap(c))
diff --git a/storage/local/persistence_test.go b/storage/local/persistence_test.go
index bc866a615..a33c5fba4 100644
--- a/storage/local/persistence_test.go
+++ b/storage/local/persistence_test.go
@@ -592,7 +592,7 @@ func testIndexing(t *testing.T, chunkType byte) {
 }
 
 func TestIndexingChunkType0(t *testing.T) {
-	testIndexing(t, 1)
+	testIndexing(t, 0)
 }
 
 func TestIndexingChunkType1(t *testing.T) {