diff --git a/osscan2.cc b/osscan2.cc
index c6584e8ae..38d3e51af 100644
--- a/osscan2.cc
+++ b/osscan2.cc
@@ -2551,7 +2551,7 @@ void HostOsScan::makeTSeqFP(HostOsScanStats *hss) {
      5) Same with ~100/sec
   */
   if (hss->si.ts_seqclass == TS_SEQ_UNKNOWN && hss->si.responses >= 2) {
-    double lastboot = 0.0;
+    time_t uptime = 0;
     avg_ts_hz = 0.0;
     for (i = 0; i < hss->si.responses - 1; i++) {
       double dhz;
@@ -2563,31 +2563,33 @@ void HostOsScan::makeTSeqFP(HostOsScanStats *hss) {
 
     if (avg_ts_hz > 0 && avg_ts_hz < 5.66) { /* relatively wide range because sampling time so short and frequency so slow */
       hss->si.ts_seqclass = TS_SEQ_2HZ;
-      lastboot = (double) hss->seq_send_times[0].tv_sec - (hss->si.timestamps[0] / 2);
-      hss->si.lastboot = hss->seq_send_times[0].tv_sec - (hss->si.timestamps[0] / 2);
+      uptime = hss->si.timestamps[0] / 2;
     }
     else if (avg_ts_hz > 70 && avg_ts_hz < 150) {
       hss->si.ts_seqclass = TS_SEQ_100HZ;
-      lastboot = (double) hss->seq_send_times[0].tv_sec - (hss->si.timestamps[0] / 100);
+      uptime = hss->si.timestamps[0] / 100;
     }
     else if (avg_ts_hz > 724 && avg_ts_hz < 1448) {
       hss->si.ts_seqclass = TS_SEQ_1000HZ;
-      lastboot = (double) hss->seq_send_times[0].tv_sec - (hss->si.timestamps[0] / 1000);
+      uptime = hss->si.timestamps[0] / 1000;
     }
     else if (avg_ts_hz > 0) {
       hss->si.ts_seqclass = TS_SEQ_OTHER_NUM;
-      lastboot = (double) hss->seq_send_times[0].tv_sec - (hss->si.timestamps[0] / (unsigned int)(0.5 + avg_ts_hz));
+      uptime = hss->si.timestamps[0] / (unsigned int)(0.5 + avg_ts_hz);
     }
 
-    if (lastboot != 0.0 && (hss->seq_send_times[0].tv_sec - lastboot > 63072000)) {
+    if (uptime > 63072000) {
       /* Up 2 years?  Perhaps, but they're probably lying. */
       if (o.debugging) {
-        log_write(LOG_STDOUT, "Ignoring claimed %s uptime of %lu days\n",
-        hss->target->targetipstr(), (hss->seq_send_times[0].tv_sec - hss->si.lastboot) / 86400);
+        /* long long is probably excessive for number of days, but sick of
+         * truncation warnings and finding the right format string for time_t
+         */
+        log_write(LOG_STDOUT, "Ignoring claimed %s uptime of %lld days\n",
+        hss->target->targetipstr(), (long long) (uptime / 86400));
       }
-      lastboot = 0;
+      uptime = 0;
     }
-    hss->si.lastboot = (long) lastboot;
+    hss->si.lastboot = hss->seq_send_times[0].tv_sec - uptime;
   }
 
   switch (hss->si.ts_seqclass) {
diff --git a/osscan2.h b/osscan2.h
index a0efda29b..f4f48a650 100644
--- a/osscan2.h
+++ b/osscan2.h
@@ -200,7 +200,7 @@ struct seq_info {
   u32 timestamps[NUM_SEQ_SAMPLES];
   int index;
   u16 ipids[NUM_SEQ_SAMPLES];
-  long lastboot; /* 0 means unknown */
+  time_t lastboot; /* 0 means unknown */
 };
 
 /* Different kinds of Ipids. */
diff --git a/output.cc b/output.cc
index e7b259162..705fd67c0 100644
--- a/output.cc
+++ b/output.cc
@@ -1989,17 +1989,17 @@ void printosscanoutput(Target *currenths) {
   if (currenths->seq.lastboot) {
     char tmbuf[128];
     struct timeval tv;
-    time_t lastboot;
-    lastboot = (time_t) currenths->seq.lastboot;
-    strncpy(tmbuf, ctime(&lastboot), sizeof(tmbuf));
+    double uptime;
+    strncpy(tmbuf, ctime(&currenths->seq.lastboot), sizeof(tmbuf));
     chomp(tmbuf);
     gettimeofday(&tv, NULL);
+    uptime = difftime(tv.tv_sec, currenths->seq.lastboot);
     if (o.verbose)
       log_write(LOG_PLAIN, "Uptime guess: %.3f days (since %s)\n",
-                (double) (tv.tv_sec - currenths->seq.lastboot) / 86400,
+                uptime / 86400,
                 tmbuf);
     xml_open_start_tag("uptime");
-    xml_attribute("seconds", "%li", tv.tv_sec - currenths->seq.lastboot);
+    xml_attribute("seconds", "%.0f", uptime);
     xml_attribute("lastboot", "%s", tmbuf);
     xml_close_empty_tag();
     xml_newline();