diff --git a/server.go b/server.go
index 3131c085..4b8cd1a0 100644
--- a/server.go
+++ b/server.go
@@ -420,10 +420,10 @@ func (s *Server) attachClient(cl *Client, listener string) error {
 		if cl.Properties.ProtocolVersion < 5 {
 			s.SendConnack(cl, packets.ErrServerUnavailable, false, nil)
 		} else {
-			s.SendConnack(cl, packets.ErrQuotaExceeded, false, nil)
+			s.SendConnack(cl, packets.ErrServerBusy, false, nil)
 		}
 
-		return packets.ErrQuotaExceeded
+		return packets.ErrServerBusy
 	}
 
 	code := s.validateConnect(cl, pk) // [MQTT-3.1.4-1] [MQTT-3.1.4-2]
diff --git a/server_test.go b/server_test.go
index bf0c1257..2a255cf4 100644
--- a/server_test.go
+++ b/server_test.go
@@ -974,7 +974,7 @@ func TestEstablishConnectionMaximumClientsReached(t *testing.T) {
 
 	err := <-o
 	require.Error(t, err)
-	require.ErrorIs(t, err, packets.ErrQuotaExceeded)
+	require.ErrorIs(t, err, packets.ErrServerBusy)
 
 	_ = r.Close()
 }