diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_HC_SR04.cpp b/libraries/AP_RangeFinder/AP_RangeFinder_HC_SR04.cpp
index 6e7cc156ec..ce7ff42dd6 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_HC_SR04.cpp
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_HC_SR04.cpp
@@ -99,7 +99,7 @@ void AP_RangeFinder_HC_SR04::update(void)
     const uint32_t now = AP_HAL::millis();
     if (value_us == 0) {
         // no reading; check for timeout:
-        if (now - last_reading_ms > 1000) {
+        if (now - state.last_reading_ms > 1000) {
             // no reading for a second - something is broken
             state.distance_m = 0.0f;
         }
@@ -125,7 +125,7 @@ void AP_RangeFinder_HC_SR04::update(void)
             glitch_count = 0;
         }
 
-        last_reading_ms = now;
+        state.last_reading_ms = now;
     }
 
     // update range_valid state based on distance measured
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_HC_SR04.h b/libraries/AP_RangeFinder/AP_RangeFinder_HC_SR04.h
index 0c582e5bfc..c5da562cdc 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_HC_SR04.h
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_HC_SR04.h
@@ -34,7 +34,6 @@ private:
     void check_trigger_pin();
 
     int8_t trigger_pin;
-    uint32_t last_reading_ms;      // system time of last read (used for health reporting)
     float last_distance_m;         // last distance reported (used to prevent glitches in measurement)
     uint8_t glitch_count;          // glitch counter
 
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.cpp b/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.cpp
index 5e600ca463..e5d6a94f00 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.cpp
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.cpp
@@ -468,6 +468,7 @@ void AP_RangeFinder_LightWareI2C::legacy_timer(void)
     if (legacy_get_reading(state.distance_m)) {
         // update range_valid state based on distance measured
         update_status();
+        state.last_reading_ms = AP_HAL::millis();
     } else {
         set_status(RangeFinder::Status::NoData);
     }
@@ -478,6 +479,7 @@ void AP_RangeFinder_LightWareI2C::sf20_timer(void)
     if (sf20_get_reading(state.distance_m)) {
         // update range_valid state based on distance measured
         update_status();
+        state.last_reading_ms = AP_HAL::millis();
     } else {
         set_status(RangeFinder::Status::NoData);
     }