diff --git a/Gaugecontroller/Gaugecontroller.ino b/Gaugecontroller/Gaugecontroller.ino
index d4e2bd2..b0fa335 100644
--- a/Gaugecontroller/Gaugecontroller.ino
+++ b/Gaugecontroller/Gaugecontroller.ino
@@ -1,5 +1,6 @@
 #include <Arduino.h>
 #include <avr/interrupt.h>
+#include <stdlib.h>
 #include <math.h>
 #include "gauge_config.h"
 
@@ -455,7 +456,8 @@ bool parseSet(const String& line) {
 bool parseSpeed(const String& line) {
   int id; char token[20];
   if (sscanf(line.c_str(), "SPEED %d %19s", &id, token) == 2) {
-    float speed = atof(token);
+    char* end; float speed = (float)strtod(token, &end);
+    if (end == token || *end != '\0') { sendReply("ERR BAD_SPEED"); return true; }
     if (id < 0 || id >= GAUGE_COUNT) { sendReply("ERR BAD_ID");    return true; }
     if (speed <= 0.0f)               { sendReply("ERR BAD_SPEED"); return true; }
     gauges[id].maxSpeed = speed;
@@ -470,7 +472,8 @@ bool parseSpeed(const String& line) {
 bool parseAccel(const String& line) {
   int id; char token[20];
   if (sscanf(line.c_str(), "ACCEL %d %19s", &id, token) == 2) {
-    float accel = atof(token);
+    char* end; float accel = (float)strtod(token, &end);
+    if (end == token || *end != '\0') { sendReply("ERR BAD_ACCEL"); return true; }
     if (id < 0 || id >= GAUGE_COUNT) { sendReply("ERR BAD_ID");    return true; }
     if (accel <= 0.0f)               { sendReply("ERR BAD_ACCEL"); return true; }
     gauges[id].accel = accel;
@@ -550,8 +553,9 @@ bool parseSweep(const String& line) {
   int id; char accelTok[20], speedTok[20];
   if (sscanf(line.c_str(), "SWEEP %d %19s %19s", &id, accelTok, speedTok) == 3) {
     if (id < 0 || id >= GAUGE_COUNT) { sendReply("ERR BAD_ID"); return true; }
-    float accel = atof(accelTok);
-    float speed = atof(speedTok);
+    char* endA; float accel = (float)strtod(accelTok, &endA);
+    char* endS; float speed = (float)strtod(speedTok, &endS);
+    if (endA == accelTok || *endA != '\0' || endS == speedTok || *endS != '\0') return false;
     Gauge& g = gauges[id];
     if (accel <= 0.0f || speed <= 0.0f) {
       g.sweepEnabled = false;