public-inbox-mda | 3 ++-

diff --git a/public-inbox-mda b/public-inbox-mda
index 72f1eac4b41f04b6f51eb2bd01bb1b4fc347c323..62d5b7fc9e51064fa97b90752a2710d6ff59a3d2 100755
--- a/public-inbox-mda
+++ b/public-inbox-mda
@@ -14,7 +14,8 @@ my $fail_repo = shift @ARGV or die "Usage: $usage\n";
 my $max = 1024 * 500; # same as spamc
 
 my $filtered;
-if (length($filter->simple->as_string) <= $max
+if ($filter->simple->header("From")
+    && length($filter->simple->as_string) <= $max
     && PublicInbox->recipient_specified($filter)
     && do_spamc($filter->simple, \$filtered)) {
 	# update our message with SA headers (in case our filter rejects it)