diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
index 47808a2a581..9a2add748e5 100644
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -290,13 +290,18 @@ BOOST_AUTO_TEST_CASE(util_TrimString)
 
 BOOST_AUTO_TEST_CASE(util_FormatISO8601DateTime)
 {
+    BOOST_CHECK_EQUAL(FormatISO8601DateTime(971890963199), "32767-12-31T23:59:59Z");
+    BOOST_CHECK_EQUAL(FormatISO8601DateTime(971890876800), "32767-12-31T00:00:00Z");
     BOOST_CHECK_EQUAL(FormatISO8601DateTime(1317425777), "2011-09-30T23:36:17Z");
     BOOST_CHECK_EQUAL(FormatISO8601DateTime(0), "1970-01-01T00:00:00Z");
 }
 
 BOOST_AUTO_TEST_CASE(util_FormatISO8601Date)
 {
+    BOOST_CHECK_EQUAL(FormatISO8601Date(971890963199), "32767-12-31");
+    BOOST_CHECK_EQUAL(FormatISO8601Date(971890876800), "32767-12-31");
     BOOST_CHECK_EQUAL(FormatISO8601Date(1317425777), "2011-09-30");
+    BOOST_CHECK_EQUAL(FormatISO8601Date(0), "1970-01-01");
 }
 
 BOOST_AUTO_TEST_CASE(util_FormatMoney)
diff --git a/src/util/time.cpp b/src/util/time.cpp
index ccb1f506100..456662bd842 100644
--- a/src/util/time.cpp
+++ b/src/util/time.cpp
@@ -3,22 +3,16 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#if defined(HAVE_CONFIG_H)
-#include <config/bitcoin-config.h>
-#endif
+#include <util/time.h>
 
 #include <compat/compat.h>
 #include <tinyformat.h>
-#include <util/time.h>
 #include <util/check.h>
 
 #include <atomic>
 #include <chrono>
-#include <ctime>
-#include <locale>
-#include <thread>
-#include <sstream>
 #include <string>
+#include <thread>
 
 void UninterruptibleSleep(const std::chrono::microseconds& n) { std::this_thread::sleep_for(n); }
 
@@ -53,30 +47,21 @@ std::chrono::seconds GetMockTime()
 
 int64_t GetTime() { return GetTime<std::chrono::seconds>().count(); }
 
-std::string FormatISO8601DateTime(int64_t nTime) {
-    struct tm ts;
-    time_t time_val = nTime;
-#ifdef HAVE_GMTIME_R
-    if (gmtime_r(&time_val, &ts) == nullptr) {
-#else
-    if (gmtime_s(&ts, &time_val) != 0) {
-#endif
-        return {};
-    }
-    return strprintf("%04i-%02i-%02iT%02i:%02i:%02iZ", ts.tm_year + 1900, ts.tm_mon + 1, ts.tm_mday, ts.tm_hour, ts.tm_min, ts.tm_sec);
+std::string FormatISO8601DateTime(int64_t nTime)
+{
+    const std::chrono::sys_seconds secs{std::chrono::seconds{nTime}};
+    const auto days{std::chrono::floor<std::chrono::days>(secs)};
+    const std::chrono::year_month_day ymd{days};
+    const std::chrono::hh_mm_ss hms{secs - days};
+    return strprintf("%04i-%02u-%02uT%02i:%02i:%02iZ", signed{ymd.year()}, unsigned{ymd.month()}, unsigned{ymd.day()}, hms.hours().count(), hms.minutes().count(), hms.seconds().count());
 }
 
-std::string FormatISO8601Date(int64_t nTime) {
-    struct tm ts;
-    time_t time_val = nTime;
-#ifdef HAVE_GMTIME_R
-    if (gmtime_r(&time_val, &ts) == nullptr) {
-#else
-    if (gmtime_s(&ts, &time_val) != 0) {
-#endif
-        return {};
-    }
-    return strprintf("%04i-%02i-%02i", ts.tm_year + 1900, ts.tm_mon + 1, ts.tm_mday);
+std::string FormatISO8601Date(int64_t nTime)
+{
+    const std::chrono::sys_seconds secs{std::chrono::seconds{nTime}};
+    const auto days{std::chrono::floor<std::chrono::days>(secs)};
+    const std::chrono::year_month_day ymd{days};
+    return strprintf("%04i-%02u-%02u", signed{ymd.year()}, unsigned{ymd.month()}, unsigned{ymd.day()});
 }
 
 struct timeval MillisToTimeval(int64_t nTimeout)