diff --git a/exports/messages.go b/exports/messages.go
index 2432dbe..6e3b7e1 100644
--- a/exports/messages.go
+++ b/exports/messages.go
@@ -28,7 +28,7 @@ func writeMessage(c *protonmail.Client, privateKeys openpgp.KeyRing, w io.Writer
 	}
 
 	mh := mail.Header{message.Header{th}}
-	mh.SetContentType(mimeType, map[string]string{"charset", "utf-8"})
+	mh.SetContentType(mimeType, map[string]string{"charset": "utf-8"})
 	mh.Set("Content-Transfer-Encoding", "quoted-printable")
 
 	// TODO: add support for attachments