diff --git a/storage/local/delta.go b/storage/local/delta.go
index 9e04890fe..ebb92e3cd 100644
--- a/storage/local/delta.go
+++ b/storage/local/delta.go
@@ -156,11 +156,11 @@ func (c deltaEncodedChunk) add(s *metric.SamplePair) []chunk {
 		case d0:
 			// No-op. Constant value is stored as base value.
 		case d1:
-			c[offset] = byte(dv)
+			c[offset] = byte(int8(dv))
 		case d2:
-			binary.LittleEndian.PutUint16(c[offset:], uint16(dv))
+			binary.LittleEndian.PutUint16(c[offset:], uint16(int16(dv)))
 		case d4:
-			binary.LittleEndian.PutUint32(c[offset:], uint32(dv))
+			binary.LittleEndian.PutUint32(c[offset:], uint32(int32(dv)))
 		// d8 must not happen. Those samples are encoded as float64.
 		default:
 			panic("invalid number of bytes for integer delta")
diff --git a/storage/local/doubledelta.go b/storage/local/doubledelta.go
index 17e2aa5f6..f11471aa5 100644
--- a/storage/local/doubledelta.go
+++ b/storage/local/doubledelta.go
@@ -164,11 +164,11 @@ func (c doubleDeltaEncodedChunk) add(s *metric.SamplePair) []chunk {
 		case d0:
 			// No-op. Constant delta is stored as base value.
 		case d1:
-			c[offset] = byte(ddv)
+			c[offset] = byte(int8(ddv))
 		case d2:
-			binary.LittleEndian.PutUint16(c[offset:], uint16(ddv))
+			binary.LittleEndian.PutUint16(c[offset:], uint16(int16(ddv)))
 		case d4:
-			binary.LittleEndian.PutUint32(c[offset:], uint32(ddv))
+			binary.LittleEndian.PutUint32(c[offset:], uint32(int32(ddv)))
 		// d8 must not happen. Those samples are encoded as float64.
 		default:
 			panic("invalid number of bytes for integer delta")