diff --git a/common/include/common.h b/common/include/common.h
index 7e2d79a..3547f35 100644
--- a/common/include/common.h
+++ b/common/include/common.h
@@ -20,7 +20,7 @@ enum return_codes {
 
 typedef struct {
     double temp;
-    uint16_t distance;
+    int32_t distance;
 } data_packet_t;
 
 // Base station radio MAC address
diff --git a/robot/include/sonar.h b/robot/include/sonar.h
index 8d22b48..b8ad087 100644
--- a/robot/include/sonar.h
+++ b/robot/include/sonar.h
@@ -17,15 +17,15 @@
 
 #define SPEED_OF_SOUND      343 // 20°C dry air (m/s)
 #define MAX_SONAR_RANGE     8 // Trigger + echo (m)
+#define MIN_SONAR_RANGE     3 // Minimum distance that is still reliable
 #define SONAR_DELAY	        60 // Timeout for return signal
 #define TIMER_MAX           65535 // For 16-bit timer
 #define CYCLES_PER_US       (F_CPU / 1000000)
 #define SONAR_TIMEOUT 	    (F_CPU * MAX_SONAR_RANGE) / SPEED_OF_SOUND
 
-#define SONAR_ERROR 0
-
+#define ECHO_TIMEOUT -1
 
 void init_sonar(void);
-uint16_t read_sonar(void);
+int32_t read_sonar(void);
 
 #endif /* SONAR_H */
diff --git a/robot/src/sonar.c b/robot/src/sonar.c
index aeaba41..8db9d31 100644
--- a/robot/src/sonar.c
+++ b/robot/src/sonar.c
@@ -12,7 +12,7 @@ void init_sonar(void)
     CLR(ECHO_DDR, ECHO_BIT);
 }
 
-uint16_t read_sonar(void)
+int32_t read_sonar(void)
 {
     // Hold high for 10us while TRIGGER sends 40KHz burst
     SET(TRIG_PORT, TRIG_BIT);
@@ -23,7 +23,7 @@ uint16_t read_sonar(void)
     // Wait for ECHO to receive TRIGGER burst
     while (!(CHK(ECHO_PIN, ECHO_BIT))) {
         if (--trig_counter == 0) {
-            return SONAR_ERROR;
+            return ECHO_TIMEOUT;
         }
     }
 
@@ -36,7 +36,7 @@ uint16_t read_sonar(void)
     // Count cycles until ECHO goes low
     while (CHK(ECHO_PIN, ECHO_BIT)) {
         if (no_of_ticks + TCNT1 > SONAR_TIMEOUT) {
-            return SONAR_ERROR;
+            return ECHO_TIMEOUT;
         }
     }
     TCCR1B = 0x00;