diff -ruN htpdate/htpdate.c htpdate.new/htpdate.c
--- htpdate/htpdate.c	2010-10-13 17:19:57.000000000 -0700
+++ new/htpdate.c	2010-10-13 17:16:06.000000000 -0700
@@ -301,9 +301,23 @@ static long getHTTPdate( char *host, cha
 	  return 0;
 }
 
+static int is_before_build_time(time_t time)
+{
+	time_t		build_time;
+	/* Is the given time before the build time? */
+	/* If no build date given, default to 0 (01 Jan 1970) */
+#ifdef BUILD_TIME_UTC
+	build_time = BUILD_TIME_UTC;
+#else
+	build_time = 0;
+#endif
+	return time < build_time;
+}
 
 static int setclock( double timedelta, int setmode ) {
-	struct timeval		timeofday;
+	struct timeval		timediff;	/* Change in time (case 1 */
+	struct timeval		timeofday;	/* Actual time of day (case 2) */
+	double			target_time;	/* Time to adjust clock to, in sec */
 
 	if ( timedelta == 0 ) {
 		printlog( 0, "No time correction needed" );
@@ -317,8 +331,20 @@ static int setclock( double timedelta, i
 		return(0);
 
 	case 1:						/* Adjust time smoothly */
-		timeofday.tv_sec  = (long)timedelta;	
-		timeofday.tv_usec = (long)((timedelta - timeofday.tv_sec) * 1000000);	
+		timediff.tv_sec  = (long)timedelta;
+		timediff.tv_usec = (long)((timedelta - timediff.tv_sec) * 1000000);
+
+		/* Check against build time */
+		gettimeofday( &timeofday, NULL );
+		target_time = timedelta + (double)timeofday.tv_sec + 1e-6 * timeofday.tv_usec;
+
+		timeofday.tv_sec  = (long)target_time;
+		timeofday.tv_usec = (long)((target_time - timeofday.tv_sec) * 1000000);
+
+		if (is_before_build_time(timeofday.tv_sec)) {
+			printlog(1, "Cannot set time to be before build time.");
+			return (-1);
+		}
 
 		printlog( 0, "Adjusting %.3f seconds", timedelta );
 
@@ -327,17 +353,22 @@ static int setclock( double timedelta, i
 			printlog( 1, "seteuid()" );
 			exit(1);
 		} else {
-			return( adjtime(&timeofday, NULL) );
+			return( adjtime(&timediff, NULL) );
 		}
 
 	case 2:					/* Set time */
 		printlog( 0, "Setting %.3f seconds", timedelta );
 
 		gettimeofday( &timeofday, NULL );
-		timedelta += ( timeofday.tv_sec + timeofday.tv_usec*1e-6 );
+		target_time = timedelta + (double)timeofday.tv_sec + 1e-6 * timeofday.tv_usec;
 
-		timeofday.tv_sec  = (long)timedelta;	
-		timeofday.tv_usec = (long)(timedelta - timeofday.tv_sec) * 1000000;	
+		timeofday.tv_sec  = (long)target_time;
+		timeofday.tv_usec = (long)((target_time - timeofday.tv_sec) * 1000000);
+
+		if (is_before_build_time(timeofday.tv_sec)) {
+			printlog(1, "Cannot set time to be before build time.");
+			return (-1);
+		}
 
 		printlog( 0, "Set: %s", asctime(localtime(&timeofday.tv_sec)) );