diff --git a/cmd/fs-v1-background-append.go b/cmd/fs-v1-background-append.go
index c7cbc626d..59de9295e 100644
--- a/cmd/fs-v1-background-append.go
+++ b/cmd/fs-v1-background-append.go
@@ -56,7 +56,7 @@ type bgAppendPartsInfo struct {
 }
 
 // Called after a part is uploaded so that it can be appended in the background.
-func (b *backgroundAppend) append(disk StorageAPI, bucket, object, uploadID string, meta fsMetaV1) {
+func (b *backgroundAppend) append(disk StorageAPI, bucket, object, uploadID string, meta fsMetaV1) chan error {
 	b.Lock()
 	info, ok := b.infoMap[uploadID]
 	if !ok {
@@ -73,21 +73,19 @@ func (b *backgroundAppend) append(disk StorageAPI, bucket, object, uploadID stri
 		go b.appendParts(disk, bucket, object, uploadID, info)
 	}
 	b.Unlock()
+	errCh := make(chan error)
 	go func() {
-		errCh := make(chan error)
 		// send input in a goroutine as send on the inputCh can block if appendParts go-routine
 		// is busy appending a part.
 		select {
 		case <-info.timeoutCh:
 			// This is to handle a rare race condition where we found info in b.infoMap
 			// but soon after that appendParts go-routine timed out.
+			errCh <- errAppendPartsTimeout
 		case info.inputCh <- bgAppendPartsInput{meta, errCh}:
-			// Receive the error so that the appendParts go-routine does not block on send.
-			// But the error received is ignored as fs.PutObjectPart() would have already
-			// returned success to the client.
-			<-errCh
 		}
 	}()
+	return errCh
 }
 
 // Called on complete-multipart-upload. Returns nil if the required parts have been appended.
@@ -153,6 +151,8 @@ func (b *backgroundAppend) appendParts(disk StorageAPI, bucket, object, uploadID
 					break
 				}
 				if err := appendPart(disk, bucket, object, uploadID, part); err != nil {
+					disk.DeleteFile(minioMetaTmpBucket, uploadID)
+					appendMeta.Parts = nil
 					input.errCh <- err
 					break
 				}
@@ -175,6 +175,7 @@ func (b *backgroundAppend) appendParts(disk StorageAPI, bucket, object, uploadID
 			disk.DeleteFile(minioMetaTmpBucket, uploadID)
 
 			close(info.timeoutCh)
+			return
 		}
 	}
 }
@@ -182,7 +183,7 @@ func (b *backgroundAppend) appendParts(disk StorageAPI, bucket, object, uploadID
 // Appends the "part" to the append-file inside "tmp/" that finally gets moved to the actual location
 // upon complete-multipart-upload.
 func appendPart(disk StorageAPI, bucket, object, uploadID string, part objectPartInfo) error {
-	partPath := pathJoin(mpartMetaPrefix, bucket, object, uploadID, part.Name)
+	partPath := pathJoin(bucket, object, uploadID, part.Name)
 
 	offset := int64(0)
 	totalLeft := part.Size
@@ -192,18 +193,15 @@ func appendPart(disk StorageAPI, bucket, object, uploadID string, part objectPar
 		if totalLeft < readSizeV1 {
 			curLeft = totalLeft
 		}
-		var n int64
 		n, err := disk.ReadFile(minioMetaMultipartBucket, partPath, offset, buf[:curLeft])
 		if err != nil {
 			// Check for EOF/ErrUnexpectedEOF not needed as it should never happen as we know
 			// the exact size of the file and hence know the size of buf[]
 			// EOF/ErrUnexpectedEOF indicates that the length of file was shorter than part.Size and
 			// hence considered as an error condition.
-			disk.DeleteFile(minioMetaTmpBucket, uploadID)
 			return err
 		}
 		if err = disk.AppendFile(minioMetaTmpBucket, uploadID, buf[:n]); err != nil {
-			disk.DeleteFile(minioMetaTmpBucket, uploadID)
 			return err
 		}
 		offset += n
diff --git a/cmd/fs-v1-multipart.go b/cmd/fs-v1-multipart.go
index d8543b189..359bebbbb 100644
--- a/cmd/fs-v1-multipart.go
+++ b/cmd/fs-v1-multipart.go
@@ -401,17 +401,30 @@ func (fs fsObjects) PutObjectPart(bucket, object, uploadID string, partID int, s
 	fsMeta.AddObjectPart(partID, partSuffix, newMD5Hex, size)
 
 	partPath := path.Join(bucket, object, uploadID, partSuffix)
+	// Lock the part so that another part upload with same part-number gets blocked
+	// while the part is getting appended in the background.
+	partLock := nsMutex.NewNSLock(minioMetaMultipartBucket, partPath)
+	partLock.Lock()
 	err = fs.storage.RenameFile(minioMetaTmpBucket, tmpPartPath, minioMetaMultipartBucket, partPath)
 	if err != nil {
+		partLock.Unlock()
 		return "", toObjectErr(traceError(err), minioMetaMultipartBucket, partPath)
 	}
 	uploadIDPath = path.Join(bucket, object, uploadID)
 	if err = writeFSMetadata(fs.storage, minioMetaMultipartBucket, path.Join(uploadIDPath, fsMetaJSONFile), fsMeta); err != nil {
+		partLock.Unlock()
 		return "", toObjectErr(err, minioMetaMultipartBucket, uploadIDPath)
 	}
 
-	// Append the part in background.
-	fs.bgAppend.append(fs.storage, bucket, object, uploadID, fsMeta)
+	go func() {
+		// Append the part in background.
+		errCh := fs.bgAppend.append(fs.storage, bucket, object, uploadID, fsMeta)
+		// Also receive the error so that the appendParts go-routine does not block on send.
+		// But the error received is ignored as fs.PutObjectPart() would have already
+		// returned success to the client.
+		<-errCh
+		partLock.Unlock()
+	}()
 
 	return newMD5Hex, nil
 }