diff --git a/backend/local.go b/backend/local.go
index 5af20e89f..c5368a69b 100644
--- a/backend/local.go
+++ b/backend/local.go
@@ -187,12 +187,19 @@ type localBlob struct {
 	tpe     Type
 	id      ID
 	size    uint
+	closed  bool
 }
 
 func (lb *localBlob) Close() error {
+	if lb.closed {
+		return errors.New("Close() called on closed file")
+
+	}
+	lb.closed = true
+
 	err := lb.f.Close()
 	if err != nil {
-		return err
+		return fmt.Errorf("local: file.Close: %v", err)
 	}
 
 	// get ID
diff --git a/backend/sftp.go b/backend/sftp.go
index 5961e43f5..712cfc82b 100644
--- a/backend/sftp.go
+++ b/backend/sftp.go
@@ -297,12 +297,18 @@ type sftpBlob struct {
 	tpe     Type
 	id      ID
 	size    uint
+	closed  bool
 }
 
 func (sb *sftpBlob) Close() error {
+	if sb.closed {
+		return errors.New("Close() called on closed file")
+	}
+	sb.closed = true
+
 	err := sb.f.Close()
 	if err != nil {
-		return err
+		return fmt.Errorf("sftp: file.Close: %v", err)
 	}
 
 	// get ID