diff --git a/libraries/AP_Proximity/AP_Proximity_LightWareSF45B.cpp b/libraries/AP_Proximity/AP_Proximity_LightWareSF45B.cpp
index 47e0e28e8e1d4..1911ea9126d2e 100644
--- a/libraries/AP_Proximity/AP_Proximity_LightWareSF45B.cpp
+++ b/libraries/AP_Proximity/AP_Proximity_LightWareSF45B.cpp
@@ -99,11 +99,11 @@ void AP_Proximity_LightWareSF45B::process_replies()
     // process up to 1K of characters per iteration
     uint32_t nbytes = MIN(_uart->available(), 1024U);
     while (nbytes-- > 0) {
-        const int16_t r = _uart->read();
-        if ((r < 0) || (r > 0xFF)) {
+        uint8_t c;
+        if (!_uart->read(c)) {
             continue;
         }
-        if (parse_byte((uint8_t)r)) {
+        if (parse_byte(c)) {
             process_message();
         }
     }
diff --git a/libraries/AP_Proximity/AP_Proximity_TeraRangerTower.cpp b/libraries/AP_Proximity/AP_Proximity_TeraRangerTower.cpp
index f467045035b32..4fe6fb6db07f8 100644
--- a/libraries/AP_Proximity/AP_Proximity_TeraRangerTower.cpp
+++ b/libraries/AP_Proximity/AP_Proximity_TeraRangerTower.cpp
@@ -65,8 +65,8 @@ bool AP_Proximity_TeraRangerTower::read_sensor_data()
     int16_t nbytes = _uart->available();
 
     while (nbytes-- > 0) {
-        int16_t c = _uart->read();
-        if (c==-1) {
+        uint8_t c;
+        if (!_uart->read(c)) {
             return false;
         }
         if (char(c) == 'T' ) {