lib/PublicInbox/Spawn.pm | 3 ++-

diff --git a/lib/PublicInbox/Spawn.pm b/lib/PublicInbox/Spawn.pm
index b02d536866836cec97ecbfc82002793fc59dbd9c..727caf1c0577663894eb88109675959decd1b39e 100644
--- a/lib/PublicInbox/Spawn.pm
+++ b/lib/PublicInbox/Spawn.pm
@@ -210,7 +210,8 @@ 		push @$rlim, $r, @$v;
 	}
 	my $cd = $opts->{'-C'} // ''; # undef => NULL mapping doesn't work?
 	my $pid = pi_fork_exec($redir, $f, $cmd, \@env, $rlim, $cd);
-	$pid < 0 ? undef : $pid;
+	die "fork_exec failed: $!\n" unless defined $pid;
+	$pid;
 }
 
 sub popen_rd {