diff --git a/git-send-email.perl b/git-send-email.perl
index 1f613fa979..caffee5dc3 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -1354,7 +1354,9 @@ sub process_address_list {
 
 sub valid_fqdn {
 	my $domain = shift;
-	return defined $domain && !($^O eq 'darwin' && $domain =~ /\.local$/) && $domain =~ /\./;
+	my $subdomain = '(?!-)[A-Za-z0-9-]{1,63}(?<!-)';
+	return defined $domain && !($^O eq 'darwin' && $domain =~ /\.local$/)
+		&& $domain  =~ /^$subdomain(?:\.$subdomain)*$/;
 }
 
 sub maildomain_net {