diff --git a/platform/mbxxx/platform-conf.h b/platform/mbxxx/platform-conf.h
index 5ed278687..cd316da82 100644
--- a/platform/mbxxx/platform-conf.h
+++ b/platform/mbxxx/platform-conf.h
@@ -85,7 +85,7 @@ typedef unsigned long clock_time_t;
 
 typedef unsigned long rtimer_clock_t;
 
-#define RTIMER_CLOCK_LT(a,b)     ((signed short)((a)-(b)) < 0)
+#define RTIMER_CLOCK_LT(a,b)     ((signed long)((a)-(b)) < 0)
 
 #define LEDS_CONF_RED_PIN     boardDescription->io->leds[1].gpioPin
 #define LEDS_CONF_GREEN_PIN   boardDescription->io->leds[0].gpioPin