diff --git a/block.go b/block.go
index 2dab0c32d..8cf28fe0e 100644
--- a/block.go
+++ b/block.go
@@ -319,7 +319,7 @@ func (pb *Block) Index() (IndexReader, error) {
 	if err := pb.startRead(); err != nil {
 		return nil, err
 	}
-	return blockIndexReader{IndexReader: pb.indexr, b: pb}, nil
+	return blockIndexReader{ir: pb.indexr, b: pb}, nil
 }
 
 // Chunks returns a new ChunkReader against the block data.
@@ -344,8 +344,40 @@ func (pb *Block) setCompactionFailed() error {
 }
 
 type blockIndexReader struct {
-	IndexReader
-	b *Block
+	ir IndexReader
+	b  *Block
+}
+
+func (r blockIndexReader) Symbols() (map[string]struct{}, error) {
+	s, err := r.ir.Symbols()
+	return s, errors.Wrapf(err, "block: %s", r.b.Meta().ULID)
+}
+
+func (r blockIndexReader) LabelValues(names ...string) (index.StringTuples, error) {
+	st, err := r.ir.LabelValues(names...)
+	return st, errors.Wrapf(err, "block: %s", r.b.Meta().ULID)
+}
+
+func (r blockIndexReader) Postings(name, value string) (index.Postings, error) {
+	p, err := r.ir.Postings(name, value)
+	return p, errors.Wrapf(err, "block: %s", r.b.Meta().ULID)
+}
+
+func (r blockIndexReader) SortedPostings(p index.Postings) index.Postings {
+	return r.ir.SortedPostings(p)
+}
+
+func (r blockIndexReader) Series(ref uint64, lset *labels.Labels, chks *[]chunks.Meta) error {
+	return errors.Wrapf(
+		r.ir.Series(ref, lset, chks),
+		"block: %s",
+		r.b.Meta().ULID,
+	)
+}
+
+func (r blockIndexReader) LabelIndices() ([][]string, error) {
+	ss, err := r.ir.LabelIndices()
+	return ss, errors.Wrapf(err, "block: %s", r.b.Meta().ULID)
 }
 
 func (r blockIndexReader) Close() error {
diff --git a/index/index.go b/index/index.go
index df8d7b5fe..a07ee8c11 100644
--- a/index/index.go
+++ b/index/index.go
@@ -585,6 +585,10 @@ func NewFileReader(path string, version int) (*Reader, error) {
 }
 
 func newReader(b ByteSlice, c io.Closer, version int) (*Reader, error) {
+	if version != 1 && version != 2 {
+		return nil, errors.Errorf("unexpected file version %d", version)
+	}
+
 	r := &Reader{
 		b:        b,
 		c:        c,
@@ -595,10 +599,6 @@ func newReader(b ByteSlice, c io.Closer, version int) (*Reader, error) {
 		version:  version,
 	}
 
-	if version != 1 && version != 2 {
-		return nil, errors.Errorf("unexpected file version %d", version)
-
-	}
 	// Verify magic number.
 	if b.Len() < 4 {
 		return nil, errors.Wrap(errInvalidSize, "index header")
@@ -674,7 +674,7 @@ func (r *Reader) readTOC() error {
 	d := decbuf{b: b[:len(b)-4]}
 
 	if d.crc32() != expCRC {
-		return errInvalidChecksum
+		return errors.Wrap(errInvalidChecksum, "read TOC")
 	}
 
 	r.toc.symbols = d.be64()
@@ -763,7 +763,7 @@ func (r *Reader) readSymbols(off int) error {
 		nextPos = basePos + uint32(origLen-d.len())
 		cnt--
 	}
-	return d.err()
+	return errors.Wrap(d.err(), "read symbols")
 }
 
 // readOffsetTable reads an offset table at the given position calls f for each
@@ -876,7 +876,7 @@ func (r *Reader) Series(id uint64, lbls *labels.Labels, chks *[]chunks.Meta) err
 	if d.err() != nil {
 		return d.err()
 	}
-	return r.dec.Series(d.get(), lbls, chks)
+	return errors.Wrap(r.dec.Series(d.get(), lbls, chks), "read series")
 }
 
 // Postings returns a postings list for the given label pair.