diff --git a/libraries/AP_Math/definitions.h b/libraries/AP_Math/definitions.h
index 0eb5250833..946c089900 100644
--- a/libraries/AP_Math/definitions.h
+++ b/libraries/AP_Math/definitions.h
@@ -100,6 +100,8 @@ static const double WGS84_E = (sqrt(2 * WGS84_F - WGS84_F * WGS84_F));
 #define AP_USEC_PER_SEC   1000000ULL
 #define AP_USEC_PER_MSEC  1000ULL
 #define AP_MSEC_PER_SEC   1000ULL
+#define AP_SEC_PER_HOUR   (3600ULL)
+#define AP_MSEC_PER_HOUR  (AP_SEC_PER_HOUR * AP_MSEC_PER_SEC)
 #define AP_SEC_PER_WEEK   (7ULL * 86400ULL)
 #define AP_MSEC_PER_WEEK  (AP_SEC_PER_WEEK * AP_MSEC_PER_SEC)