diff --git a/src/NeoTime.h b/src/NeoTime.h
index e9ba767..06c4586 100644
--- a/src/NeoTime.h
+++ b/src/NeoTime.h
@@ -41,7 +41,9 @@ const uint8_t  MINUTES_PER_HOUR   = 60;
 const uint16_t SECONDS_PER_HOUR   = (uint16_t) SECONDS_PER_MINUTE * MINUTES_PER_HOUR;
 const uint8_t  HOURS_PER_DAY      = 24;
 const uint32_t SECONDS_PER_DAY    = (uint32_t) SECONDS_PER_HOUR * HOURS_PER_DAY;
-const uint8_t  DAYS_PER_WEEK      = 7;
+#ifndef DAYS_PER_WEEK
+	const uint8_t  DAYS_PER_WEEK      = 7;
+#endif
 
 /**
  * Common date/time structure
@@ -192,7 +194,7 @@ struct time_t {
    */
   static uint8_t weekday_for(uint16_t dayno)
   {
-    return ((dayno+epoch_weekday()-1) % DAYS_PER_WEEK) + 1;
+    return ((dayno+epoch_weekday()-1) % (uint8_t)DAYS_PER_WEEK) + 1;
   }
 
   /**