diff --git a/libraries/AP_GPS/AP_GPS.cpp b/libraries/AP_GPS/AP_GPS.cpp
index 1e94fa810c..42009f7e3e 100644
--- a/libraries/AP_GPS/AP_GPS.cpp
+++ b/libraries/AP_GPS/AP_GPS.cpp
@@ -763,7 +763,14 @@ AP_GPS_Backend *AP_GPS::_detect_instance(uint8_t instance)
             dstate->current_baud = 0;
         }
         uint32_t baudrate = _baudrates[dstate->current_baud];
-        _port[instance]->begin(baudrate);
+        uint16_t rx_size=0, tx_size=0;
+        if (_type[instance] == GPS_TYPE_UBLOX_RTK_ROVER) {
+            tx_size = 2048;
+        }
+        if (_type[instance] == GPS_TYPE_UBLOX_RTK_BASE) {
+            rx_size = 2048;
+        }
+        _port[instance]->begin(baudrate, rx_size, tx_size);
         _port[instance]->set_flow_control(AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE);
         dstate->last_baud_change_ms = now;