diff --git a/main.go b/main.go
index a8acc18..bc81384 100644
--- a/main.go
+++ b/main.go
@@ -357,7 +357,7 @@ func (server *Server) objectExists(dn string) (bool, error) {
 func (server *Server) checkSuffix(dn string, allow_extend bool) (string, error) {
 	suffix := server.config.Suffix
 	if len(dn) < len(suffix) {
-		if dn != suffix[-len(dn):] || !allow_extend {
+		if dn != suffix[len(suffix)-len(dn):] || !allow_extend {
 			return suffix, fmt.Errorf(
 				"Only handling stuff under DN %s", suffix)
 		}