diff --git a/libraries/AP_Proximity/AP_Proximity_Cygbot_D1.cpp b/libraries/AP_Proximity/AP_Proximity_Cygbot_D1.cpp
index 25a0ed8a81..5a81f3fe4a 100644
--- a/libraries/AP_Proximity/AP_Proximity_Cygbot_D1.cpp
+++ b/libraries/AP_Proximity/AP_Proximity_Cygbot_D1.cpp
@@ -43,7 +43,7 @@ void AP_Proximity_Cygbot_D1::read_sensor_data()
 {
     uint32_t nbytes = _uart->available();
     while (nbytes-- > 0) {
-        uint8_t byte = _uart->read();
+        int16_t byte = _uart->read();
         if (!parse_byte(byte)) {
             // reset
             reset();
diff --git a/libraries/AP_Proximity/AP_Proximity_RPLidarA2.cpp b/libraries/AP_Proximity/AP_Proximity_RPLidarA2.cpp
index 63d4c82230..ab3d1ad05a 100644
--- a/libraries/AP_Proximity/AP_Proximity_RPLidarA2.cpp
+++ b/libraries/AP_Proximity/AP_Proximity_RPLidarA2.cpp
@@ -163,7 +163,7 @@ void AP_Proximity_RPLidarA2::get_readings()
 
     while (nbytes-- > 0) {
 
-        uint8_t c = _uart->read();
+        int16_t c = _uart->read();
         Debug(2, "UART READ %x <%c>", c, c); //show HEX values
 
         STATE:
diff --git a/libraries/AP_Proximity/AP_Proximity_TeraRangerTower.cpp b/libraries/AP_Proximity/AP_Proximity_TeraRangerTower.cpp
index 3c7119726a..a5c2027c35 100644
--- a/libraries/AP_Proximity/AP_Proximity_TeraRangerTower.cpp
+++ b/libraries/AP_Proximity/AP_Proximity_TeraRangerTower.cpp
@@ -62,8 +62,11 @@ bool AP_Proximity_TeraRangerTower::read_sensor_data()
     int16_t nbytes = _uart->available();
 
     while (nbytes-- > 0) {
-        char c = _uart->read();
-        if (c == 'T' ) {
+        int16_t c = _uart->read();
+        if (c==-1) {
+            return false;
+        }
+        if (char(c) == 'T' ) {
             buffer_count = 0;
         }
 
diff --git a/libraries/AP_Proximity/AP_Proximity_TeraRangerTowerEvo.cpp b/libraries/AP_Proximity/AP_Proximity_TeraRangerTowerEvo.cpp
index e9aceee786..db527417df 100644
--- a/libraries/AP_Proximity/AP_Proximity_TeraRangerTowerEvo.cpp
+++ b/libraries/AP_Proximity/AP_Proximity_TeraRangerTowerEvo.cpp
@@ -116,8 +116,11 @@ bool AP_Proximity_TeraRangerTowerEvo::read_sensor_data()
     }
 
     while (nbytes-- > 0) {
-        char c = _uart->read();
-        if (c == 'T' ) {
+        int16_t c = _uart->read();
+        if (c==-1) {
+            return false;
+        }
+        if (char(c) == 'T' ) {
             buffer_count = 0;
         }
         buffer[buffer_count++] = c;