diff --git a/chunks/chunks.go b/chunks/chunks.go
index 9c80767ff7..795740ff3e 100644
--- a/chunks/chunks.go
+++ b/chunks/chunks.go
@@ -296,7 +296,7 @@ func newReader(bs []ByteSlice, cs []io.Closer, pool chunkenc.Pool) (*Reader, err
 		}
 		// Verify magic number.
 		if m := binary.BigEndian.Uint32(b.Range(0, 4)); m != MagicChunks {
-			return nil, fmt.Errorf("invalid magic number %x", m)
+			return nil, errors.Errorf("invalid magic number %x", m)
 		}
 	}
 	return &cr, nil
@@ -357,8 +357,8 @@ func (s *Reader) Chunk(ref uint64) (chunkenc.Chunk, error) {
 	r := b.Range(off, off+binary.MaxVarintLen32)
 
 	l, n := binary.Uvarint(r)
-	if n < 0 {
-		return nil, fmt.Errorf("reading chunk length failed")
+	if n <= 0 {
+		return nil, errors.Errorf("reading chunk length failed with %d", n)
 	}
 	r = b.Range(off+n, off+n+int(l))
 
diff --git a/chunks/chunks_test.go b/chunks/chunks_test.go
new file mode 100644
index 0000000000..e153029b71
--- /dev/null
+++ b/chunks/chunks_test.go
@@ -0,0 +1,28 @@
+// Copyright 2017 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package chunks
+
+import (
+	"testing"
+
+	"github.com/prometheus/tsdb/testutil"
+)
+
+func TestReaderWithInvalidBuffer(t *testing.T) {
+	b := realByteSlice([]byte{0x81, 0x81, 0x81, 0x81, 0x81, 0x81})
+	r := &Reader{bs: []ByteSlice{b}}
+
+	_, err := r.Chunk(0)
+	testutil.NotOk(t, err)
+}
diff --git a/index/index.go b/index/index.go
index 72ca3835ae..c58ff6ea83 100644
--- a/index/index.go
+++ b/index/index.go
@@ -740,8 +740,8 @@ func (r *Reader) decbufUvarintAt(off int) decbuf {
 	b := r.b.Range(off, off+binary.MaxVarintLen32)
 
 	l, n := binary.Uvarint(b)
-	if n > binary.MaxVarintLen32 {
-		return decbuf{e: errors.New("invalid uvarint")}
+	if n <= 0 || n > binary.MaxVarintLen32 {
+		return decbuf{e: errors.Errorf("invalid uvarint %d", n)}
 	}
 
 	if r.b.Len() < off+n+int(l)+4 {
diff --git a/index/index_test.go b/index/index_test.go
index f1b4d41817..8d71981361 100644
--- a/index/index_test.go
+++ b/index/index_test.go
@@ -380,3 +380,11 @@ func TestPersistence_index_e2e(t *testing.T) {
 
 	testutil.Ok(t, ir.Close())
 }
+
+func TestReaderWithInvalidBuffer(t *testing.T) {
+	b := realByteSlice([]byte{0x81, 0x81, 0x81, 0x81, 0x81, 0x81})
+	r := &Reader{b: b}
+
+	db := r.decbufUvarintAt(0)
+	testutil.NotOk(t, db.err())
+}