diff --git a/pkg/blobserver/diskpacked/diskpacked.go b/pkg/blobserver/diskpacked/diskpacked.go
index 01ea73feb..6803d99bb 100644
--- a/pkg/blobserver/diskpacked/diskpacked.go
+++ b/pkg/blobserver/diskpacked/diskpacked.go
@@ -649,6 +649,8 @@ func (s *storage) append(br blob.SizedRef, r io.Reader) error {
 	if s.closed {
 		return errors.New("diskpacked: write to closed storage")
 	}
+	// to be able to undo the append
+	origOffset := s.size
 
 	fn := s.writer.Name()
 	n, err := fmt.Fprintf(s.writer, "[%v %v]", br.Ref.String(), br.Size)
@@ -690,7 +692,17 @@ func (s *storage) append(br blob.SizedRef, r io.Reader) error {
 			return err
 		}
 	}
-	return s.index.Set(br.Ref.String(), blobMeta{packIdx, offset, br.Size}.String())
+	err = s.index.Set(br.Ref.String(), blobMeta{packIdx, offset, br.Size}.String())
+	if err != nil {
+		if _, seekErr := s.writer.Seek(origOffset, os.SEEK_SET); seekErr != nil {
+			log.Printf("ERROR seeking back to the original offset: %v", seekErr)
+		} else if truncErr := s.writer.Truncate(origOffset); truncErr != nil {
+			log.Printf("ERROR truncating file after index error: %v", truncErr)
+		} else {
+			s.size = origOffset
+		}
+	}
+	return err
 }
 
 // meta fetches the metadata for the specified blob from the index.
diff --git a/pkg/blobserver/diskpacked/diskpacked_test.go b/pkg/blobserver/diskpacked/diskpacked_test.go
index 8326c27ae..5d22303ff 100644
--- a/pkg/blobserver/diskpacked/diskpacked_test.go
+++ b/pkg/blobserver/diskpacked/diskpacked_test.go
@@ -17,6 +17,7 @@ limitations under the License.
 package diskpacked
 
 import (
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -27,6 +28,7 @@ import (
 	"camlistore.org/pkg/blobserver"
 	"camlistore.org/pkg/blobserver/storagetest"
 	"camlistore.org/pkg/jsonconfig"
+	"camlistore.org/pkg/sorted"
 	"camlistore.org/pkg/test"
 )
 
@@ -196,3 +198,57 @@ func TestDelete(t *testing.T) {
 		}
 	}
 }
+
+var dummyErr = errors.New("dummy fail")
+
+func TestDoubleReceiveFailingIndex(t *testing.T) {
+	sto, cleanup := newTempDiskpacked(t)
+	defer cleanup()
+
+	sto.(*storage).index = &failingIndex{KeyValue: sto.(*storage).index}
+
+	size := func(n int) int64 {
+		path := sto.(*storage).filename(n)
+		fi, err := os.Stat(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return fi.Size()
+	}
+
+	const blobSize = 5 << 10
+	b := &test.Blob{Contents: strings.Repeat("a", blobSize)}
+	br := b.BlobRef()
+
+	_, err := blobserver.Receive(sto, br, b.Reader())
+	if err != nil {
+		if err != dummyErr {
+			t.Fatal(err)
+		}
+		t.Logf("dummy fail")
+	}
+	if size(0) >= blobSize {
+		t.Fatalf("size = %d; want zero (at most %d)", size(0), blobSize-1)
+	}
+
+	_, err = blobserver.Receive(sto, br, b.Reader())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if size(0) < blobSize {
+		t.Fatalf("size = %d; want at least %d", size(0), blobSize)
+	}
+}
+
+type failingIndex struct {
+	sorted.KeyValue
+	setCount int
+}
+
+func (idx *failingIndex) Set(key string, value string) error {
+	idx.setCount++
+	if idx.setCount == 1 { // fail the first time
+		return dummyErr
+	}
+	return idx.KeyValue.Set(key, value)
+}
diff --git a/pkg/blobserver/diskpacked/reindex.go b/pkg/blobserver/diskpacked/reindex.go
index f3efe6ee9..f83a83613 100644
--- a/pkg/blobserver/diskpacked/reindex.go
+++ b/pkg/blobserver/diskpacked/reindex.go
@@ -81,6 +81,7 @@ func (s *storage) reindexOne(ctx *context.Context, index sorted.KeyValue, overwr
 
 	// TODO(tgulacsi): proper verbose from context
 	verbose := camliDebug
+	misses := make(map[blob.Ref]string, 8)
 	err := s.walkPack(verbose, packID,
 		func(packID int, ref blob.Ref, offset int64, size uint32) error {
 			if !ref.Valid() {
@@ -92,17 +93,25 @@ func (s *storage) reindexOne(ctx *context.Context, index sorted.KeyValue, overwr
 			meta := blobMeta{packID, offset, size}.String()
 			if overwrite && batch != nil {
 				batch.Set(ref.String(), meta)
-			} else {
-				if old, err := index.Get(ref.String()); err != nil {
+				return nil
+			}
+			if _, ok := misses[ref]; ok { // maybe this is the last of this blob.
+				delete(misses, ref)
+			}
+			if old, err := index.Get(ref.String()); err != nil {
+				allOk = false
+				if err == sorted.ErrNotFound {
+					log.Println(ref.String() + ": cannot find in index!")
+				} else {
+					log.Println(ref.String()+": error getting from index: ", err.Error())
+				}
+			} else if old != meta {
+				if old > meta {
+					misses[ref] = meta
+					log.Printf("WARN: possible duplicate blob %s", ref.String())
+				} else {
 					allOk = false
-					if err == sorted.ErrNotFound {
-						log.Println(ref.String() + ": cannot find in index!")
-					} else {
-						log.Println(ref.String()+": error getting from index: ", err.Error())
-					}
-				} else if old != meta {
-					allOk = false
-					log.Printf("%s: index mismatch - index=%s data=%s", ref.String(), old, meta)
+					log.Printf("ERROR: index mismatch for %s - index=%s, meta=%s!", ref.String(), old, meta)
 				}
 			}
 			return nil
@@ -111,6 +120,11 @@ func (s *storage) reindexOne(ctx *context.Context, index sorted.KeyValue, overwr
 		return err
 	}
 
+	for ref, meta := range misses {
+		log.Printf("ERROR: index mismatch for %s (%s)!", ref.String(), meta)
+		allOk = false
+	}
+
 	if overwrite && batch != nil {
 		log.Printf("overwriting %s from %d", index, packID)
 		if err = index.CommitBatch(batch); err != nil {