diff --git a/attachment/attachment.go b/attachment/attachment.go
index ac4573e..cc6eadf 100644
--- a/attachment/attachment.go
+++ b/attachment/attachment.go
@@ -170,16 +170,16 @@ func ResolveLocalAttachments(opener vfs.Opener, base string, replacements []stri
 		return nil, err
 	}
 
-	for _, attachment := range attachments {
-		checksum, err := GetChecksum(bytes.NewReader(attachment.FileBytes))
+	for i := range attachments {
+		checksum, err := GetChecksum(bytes.NewReader(attachments[i].FileBytes))
 		if err != nil {
 			return nil, karma.Format(
 				err,
-				"unable to get checksum for attachment: %q", attachment.Name,
+				"unable to get checksum for attachment: %q", attachments[i].Name,
 			)
 		}
 
-		attachment.Checksum = checksum
+		attachments[i].Checksum = checksum
 	}
 	return attachments, err
 }
diff --git a/attachment/attachment_test.go b/attachment/attachment_test.go
index c3dc547..ac290dc 100644
--- a/attachment/attachment_test.go
+++ b/attachment/attachment_test.go
@@ -27,7 +27,7 @@ type virtualOpener struct {
 	PathToBuf map[string]*bufferCloser
 }
 
-func (o *virtualOpener) Open(name string) (io.ReadWriteCloser, error) {
+func (o *virtualOpener) Open(name string) (io.ReadCloser, error) {
 	if buf, ok := o.PathToBuf[name]; ok {
 		return buf, nil
 	}