diff --git a/tsdb/chunkenc/chunk.go b/tsdb/chunkenc/chunk.go
index 2bc1bf33f..5f228df48 100644
--- a/tsdb/chunkenc/chunk.go
+++ b/tsdb/chunkenc/chunk.go
@@ -41,14 +41,28 @@ const (
 
 // Chunk holds a sequence of sample pairs that can be iterated over and appended to.
 type Chunk interface {
+	// Bytes returns the underlying byte slice of the chunk.
 	Bytes() []byte
+
+	// Encoding returns the encoding type of the chunk.
 	Encoding() Encoding
+
+	// Appender returns an appender to append samples to the chunk.
 	Appender() (Appender, error)
+
 	// The iterator passed as argument is for re-use.
 	// Depending on implementation, the iterator can
 	// be re-used or a new iterator can be allocated.
 	Iterator(Iterator) Iterator
+
+	// NumSamples returns the number of samples in the chunk.
 	NumSamples() int
+
+	// Compact is called whenever a chunk is expected to be complete (no more
+	// samples appended) and the underlying implementation can eventually
+	// optimize the chunk.
+	// There's no strong guarantee that no samples will be appended once
+	// Compact() is called. Implementing this function is optional.
 	Compact()
 }