diff --git a/grbl/cpu_map/cpu_map_atmega328p.h b/grbl/cpu_map/cpu_map_atmega328p.h
index 702378cc9..209508e17 100644
--- a/grbl/cpu_map/cpu_map_atmega328p.h
+++ b/grbl/cpu_map/cpu_map_atmega328p.h
@@ -71,7 +71,7 @@
 #else
   #define Z_LIMIT_BIT    4  // Uno Digital Pin 11
 #endif
-#define LIMIT_MASK       ((0<<X_LIMIT_BIT)|(0<<Y_LIMIT_BIT)|(0<<Z_LIMIT_BIT)) // All limit bits
+#define LIMIT_MASK       ((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)|(1<<Z_LIMIT_BIT)) // All limit bits
 #define LIMIT_INT        PCIE0  // Pin change interrupt enable pin
 #define LIMIT_INT_vect   PCINT0_vect 
 #define LIMIT_PCMSK      PCMSK0 // Pin change interrupt register