diff --git a/libraries/AP_GPS/AP_GPS.cpp b/libraries/AP_GPS/AP_GPS.cpp
index da0e75ea37..2bb094cbef 100644
--- a/libraries/AP_GPS/AP_GPS.cpp
+++ b/libraries/AP_GPS/AP_GPS.cpp
@@ -1757,7 +1757,9 @@ bool AP_GPS::is_healthy(uint8_t instance) const
     const uint8_t delay_threshold = 2;
     const float delay_avg_max = _type[instance] == GPS_TYPE_UBLOX_RTK_ROVER?245:215;
     const GPS_timing &t = timing[instance];
-    bool delay_ok = (t.delayed_count < delay_threshold) && t.average_delta_ms < delay_avg_max;
+    bool delay_ok = (t.delayed_count < delay_threshold) &&
+        t.average_delta_ms < delay_avg_max &&
+        state[instance].lagged_sample_count < 5;
 
 #if defined(GPS_BLENDED_INSTANCE)
     if (instance == GPS_BLENDED_INSTANCE) {
diff --git a/libraries/AP_GPS/AP_GPS.h b/libraries/AP_GPS/AP_GPS.h
index 1368510e73..0a171a0cdc 100644
--- a/libraries/AP_GPS/AP_GPS.h
+++ b/libraries/AP_GPS/AP_GPS.h
@@ -173,6 +173,7 @@ public:
         bool have_gps_yaw_accuracy;       ///< does the GPS give a heading accuracy estimate? Set to true only once available
         uint32_t last_gps_time_ms;          ///< the system time we got the last GPS timestamp, milliseconds
         uint32_t uart_timestamp_ms;         ///< optional timestamp from set_uart_timestamp()
+        uint32_t lagged_sample_count;       ///< number of samples with 50ms more lag than expected
 
         // all the following fields must only all be filled by RTK capable backend drivers
         uint32_t rtk_time_week_ms;         ///< GPS Time of Week of last baseline in milliseconds
diff --git a/libraries/AP_GPS/GPS_Backend.cpp b/libraries/AP_GPS/GPS_Backend.cpp
index 1a64e3730f..a60f83e710 100644
--- a/libraries/AP_GPS/GPS_Backend.cpp
+++ b/libraries/AP_GPS/GPS_Backend.cpp
@@ -287,5 +287,19 @@ void AP_GPS_Backend::check_new_itow(uint32_t itow, uint32_t msg_length)
         // use msg arrival time, and correct for jitter
         uint64_t local_us = jitter_correction.correct_offboard_timestamp_usec(_pseudo_itow, uart_us);
         state.uart_timestamp_ms = local_us / 1000U;
+
+        // look for lagged data from the GPS. This is meant to detect
+        // the case that the GPS is trying to push more data into the
+        // UART than can fit (eg. with GPS_RAW_DATA at 115200).
+        float expected_lag;
+        if (gps.get_lag(state.instance, expected_lag)) {
+            float lag_s = (now - state.uart_timestamp_ms) * 0.001;
+            if (lag_s > expected_lag+0.05) {
+                // more than 50ms over expected lag, increment lag counter
+                state.lagged_sample_count++;
+            } else {
+                state.lagged_sample_count = 0;
+            }
+        }
     }
 }