diff --git a/MimeKit/BodyBuilder.cs b/MimeKit/BodyBuilder.cs
index d4802e82ff..1156a8dfa1 100644
--- a/MimeKit/BodyBuilder.cs
+++ b/MimeKit/BodyBuilder.cs
@@ -166,6 +166,9 @@ public MimeEntity ToMessageBody ()
 			}
 
 			if (Attachments.Count > 0) {
+				if (body == null && Attachments.Count == 1)
+					return Attachments[0];
+
 				var mixed = new Multipart ("mixed");
 
 				if (body != null)