diff --git a/sys/src/cmd/upas/Mail/mbox.c b/sys/src/cmd/upas/Mail/mbox.c
index 60fdc7dee..b7bdeda83 100644
--- a/sys/src/cmd/upas/Mail/mbox.c
+++ b/sys/src/cmd/upas/Mail/mbox.c
@@ -802,6 +802,8 @@ changemesg(Plumbmsg *pm)
 
 	digest = plumblookup(pm->attr, "digest");
 	action = plumblookup(pm->attr, "mailtype");
+	if(digest == nil || action == nil)
+		return;
 	if(strcmp(action, "new") == 0){
 		if((m = load(pm->data, digest, 1)) == nil)
 			return;