diff --git a/web/server.go b/web/server.go
index 9b49993..15c2d82 100644
--- a/web/server.go
+++ b/web/server.go
@@ -946,7 +946,7 @@ func (s *Server) handleValidateCarNumber() http.HandlerFunc {
 		if !isUnique {
 			w.Write([]byte("<div id='car-number-validation-error' class='alert alert-danger'>Car number is already in use</div>"))
 		} else {
-			w.Write([]byte("<div id='car-number-validation-error'></div>"))
+			w.Write([]byte("<div class='invalid-feedback' id='car-number-validation-error'></div>"))
 		}
 	}
 }