diff --git a/Readme.md b/Readme.md
index 7556e0d..86add2c 100644
--- a/Readme.md
+++ b/Readme.md
@@ -53,7 +53,8 @@ year(t);          // the year for the given time t
 There are also two functions that return the number of milliseconds left-over. Care
 should be taken when using this value since there are no functions to set the time
 with sub-second accuracy and the value may jump when the time is synchronized.
-However, it is always consistent with the current time.
+However, it is always consistent with the current time. To access these functions,
+you have to `#define TIMELIB_ENABLE_MILLIS` in your sketch.
 
 ```c
 time_t t = now(uint32_t& m) // store the current time in time variable t and milliseconds in m
diff --git a/Time.cpp b/Time.cpp
index bd3cc7b..fd07a57 100644
--- a/Time.cpp
+++ b/Time.cpp
@@ -33,6 +33,7 @@
 #include <WProgram.h> 
 #endif
 
+#define TIMELIB_ENABLE_MILLIS
 #include "TimeLib.h"
 
 static tmElements_t tm;          // a cache of time elements
diff --git a/TimeLib.h b/TimeLib.h
index 75ff482..38cfa2c 100644
--- a/TimeLib.h
+++ b/TimeLib.h
@@ -108,7 +108,9 @@ int     minute();          // the minute now
 int     minute(time_t t);  // the minute for the given time
 int     second();          // the second now 
 int     second(time_t t);  // the second for the given time
+#ifdef TIMELIB_ENABLE_MILLIS
 int     millisecond();     // the millisecond now
+#endif
 int     day();             // the day now 
 int     day(time_t t);     // the day for the given time
 int     weekday();         // the weekday now (Sunday is day 1) 
@@ -119,7 +121,9 @@ int     year();            // the full four digit year: (2009, 2010 etc)
 int     year(time_t t);    // the year for the given time
 
 time_t now();              // return the current time as seconds since Jan 1 1970 
+#ifdef TIMELIB_ENABLE_MILLIS
 time_t now(uint32_t& sysTimeMillis); // return the current time as seconds and milliseconds since Jan 1 1970
+#endif
 void    setTime(time_t t);
 void    setTime(int hr,int min,int sec,int day, int month, int yr);
 void    adjustTime(long adjustment);