diff --git a/tmk_core/common/timer.h b/tmk_core/common/timer.h
index fe23f87a..a8c50fe7 100644
--- a/tmk_core/common/timer.h
+++ b/tmk_core/common/timer.h
@@ -25,7 +25,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #endif
 
 
-#define TIMER_DIFF(a, b, max)   ((a) >= (b) ?  (a) - (b) : (max) - (b) + (a))
+#define TIMER_DIFF(a, b, max)   ((a) >= (b) ?  (a) - (b) : (max) + 1 - (b) + (a))
 #define TIMER_DIFF_8(a, b)      TIMER_DIFF(a, b, UINT8_MAX)
 #define TIMER_DIFF_16(a, b)     TIMER_DIFF(a, b, UINT16_MAX)
 #define TIMER_DIFF_32(a, b)     TIMER_DIFF(a, b, UINT32_MAX)