diff --git a/configure b/configure
index cde0e17..e4dab64 100755
--- a/configure
+++ b/configure
@@ -114,6 +114,8 @@ For better control, use the options below.
   --disable-linuxcaps    Disable Linux capabilities support
   --disable-asyncdns     Disable asynchronous name resolving
   --disable-forcednsretry Don't retry on permanent DNS error
+  --with-ntp-era=SECONDS Specify earliest assumed NTP time in seconds
+                         since 1970-01-01 [50*365 days ago]
   --with-user=USER       Specify default chronyd user [root]
   --with-sendmail=PATH   Path to sendmail binary [/usr/lib/sendmail]
   --enable-debug         Enable debugging support
@@ -194,6 +196,7 @@ try_setsched=0
 try_lockmem=0
 feat_asyncdns=1
 feat_forcednsretry=1
+ntp_era_split=""
 default_user="root"
 mail_program="/usr/lib/sendmail"
 
@@ -275,6 +278,9 @@ do
     --disable-forcednsretry)
       feat_forcednsretry=0
     ;;
+    --with-ntp-era=* )
+      ntp_era_split=`echo $option | sed -e 's/^.*=//;'`
+    ;;
     --with-user=* )
       default_user=`echo $option | sed -e 's/^.*=//;'`
     ;;
@@ -381,6 +387,33 @@ if test_code '64-bit time_t' 'time.h' '' '' '
   return x[0];'
 then
   add_def HAVE_LONG_TIME_T 1
+
+  if [ "x$ntp_era_split" != "x" ]; then
+    split_seconds=$ntp_era_split
+    split_days=0
+  else
+    split_seconds=`date '+%s'`
+    if [ "x$split_seconds" = "" ]; then
+      echo "Could not get current time, --with-ntp-era option is needed"
+      exit 1
+    fi
+    split_days=$((50 * 365))
+  fi
+
+  add_def NTP_ERA_SPLIT "(${split_seconds}LL - $split_days * 24 * 3600)"
+
+  date_format='+%Y-%m-%dT%H:%M:%SZ'
+
+  # Print the full NTP interval if a suitable date is found
+  if [ "x`date -u -d '1970-01-01 UTC 9 days ago 5 seconds 3 seconds' \
+    $date_format 2> /dev/null`" = "x1969-12-23T00:00:08Z" ]
+  then
+    time1="`date -u -d "1970-01-01 UTC $split_days days ago $split_seconds seconds" \
+      $date_format`"
+    time2="`date -u -d "1970-01-01 UTC $split_days days ago $split_seconds seconds 4294967296 seconds" \
+      $date_format`"
+    echo "NTP time mapped to $time1/$time2"
+  fi
 fi
 
 MATHCODE='return (int) pow(2.0, log(sqrt((double)argc)));'
diff --git a/ntp_core.c b/ntp_core.c
index c83f1e8..278b804 100644
--- a/ntp_core.c
+++ b/ntp_core.c
@@ -258,10 +258,35 @@ do_size_checks(void)
 
 /* ================================================== */
 
+static void
+do_time_checks(void)
+{
+#ifdef HAVE_LONG_TIME_T
+  /* Check that time before NTP_ERA_SPLIT underflows correctly */
+
+  struct timeval tv1 = {NTP_ERA_SPLIT, 1}, tv2 = {NTP_ERA_SPLIT - 1, 1};
+  NTP_int64 ntv1, ntv2;
+  int r;
+
+  UTI_TimevalToInt64(&tv1, &ntv1, 0);
+  UTI_TimevalToInt64(&tv2, &ntv2, 0);
+  UTI_Int64ToTimeval(&ntv1, &tv1);
+  UTI_Int64ToTimeval(&ntv2, &tv2);
+
+  r = tv1.tv_sec == NTP_ERA_SPLIT &&
+      tv1.tv_sec + (1ULL << 32) - 1 == tv2.tv_sec;
+
+  assert(r);
+#endif
+}
+
+/* ================================================== */
+
 void
 NCR_Initialise(void)
 {
   do_size_checks();
+  do_time_checks();
 
   logfileid = CNF_GetLogMeasurements() ? LOG_FileOpen("measurements",
       "   Date (UTC) Time     IP Address   L St 1234 abc 5678 LP RP Score Offset     Peer del. Peer disp. Root del.  Root disp.")
diff --git a/util.c b/util.c
index 35bc12b..e1d314e 100644
--- a/util.c
+++ b/util.c
@@ -498,16 +498,17 @@ void
 UTI_TimevalToInt64(struct timeval *src,
                    NTP_int64 *dest, uint32_t fuzz)
 {
-  unsigned long usec = src->tv_usec;
-  unsigned long sec = src->tv_sec;
-  uint32_t lo;
+  uint32_t lo, sec, usec;
+
+  sec = (uint32_t)src->tv_sec;
+  usec = (uint32_t)src->tv_usec;
 
   /* Recognize zero as a special case - it always signifies
      an 'unknown' value */
   if (!usec && !sec) {
     dest->hi = dest->lo = 0;
   } else {
-    dest->hi = htonl(src->tv_sec + JAN_1970);
+    dest->hi = htonl(sec + JAN_1970);
 
     /* This formula gives an error of about 0.1us worst case */
     lo = 4295 * usec - (usec>>5) - (usec>>9);
@@ -525,13 +526,23 @@ void
 UTI_Int64ToTimeval(NTP_int64 *src,
                    struct timeval *dest)
 {
+  uint32_t ntp_sec, ntp_frac;
+
   /* As yet, there is no need to check for zero - all processing that
      has to detect that case is in the NTP layer */
 
-  dest->tv_sec = ntohl(src->hi) - JAN_1970;
+  ntp_sec = ntohl(src->hi);
+  ntp_frac = ntohl(src->lo);
+
+#ifdef HAVE_LONG_TIME_T
+  dest->tv_sec = ntp_sec - (uint32_t)(NTP_ERA_SPLIT + JAN_1970) +
+                 (time_t)NTP_ERA_SPLIT;
+#else
+  dest->tv_sec = ntp_sec - JAN_1970;
+#endif
   
   /* Until I invent a slick way to do this, just do it the obvious way */
-  dest->tv_usec = (int)(0.5 + (double)(ntohl(src->lo)) / 4294.967296);
+  dest->tv_usec = (int)(0.5 + (double)(ntp_frac) / 4294.967296);
 }
 
 /* ================================================== */