diff --git a/libraries/SITL/SIM_FETtecOneWireESC.cpp b/libraries/SITL/SIM_FETtecOneWireESC.cpp
index 4af2bdb33d..c59b4f3588 100644
--- a/libraries/SITL/SIM_FETtecOneWireESC.cpp
+++ b/libraries/SITL/SIM_FETtecOneWireESC.cpp
@@ -384,7 +384,7 @@ void FETtecOneWireESC::consume_bytes(uint8_t count)
 
 void FETtecOneWireESC::update_input()
 {
-    const ssize_t n = read_from_autopilot((char*)&u.buffer[buflen], ARRAY_SIZE(u.buffer) - buflen - 1);
+    const ssize_t n = read_from_autopilot((char*)&u.buffer[buflen], ARRAY_SIZE(u.buffer) - buflen);
     if (n < 0) {
         // TODO: do better here
         if (errno != EAGAIN && errno != EWOULDBLOCK && errno != 0) {