diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -144,23 +144,6 @@
         "1feae06279a60939e028a8d65c10b73071a6f16719274855feb0fd8a6704");
 }
 
-BOOST_AUTO_TEST_CASE(util_DateTimeStrFormat) {
-    BOOST_CHECK_EQUAL(DateTimeStrFormat("%Y-%m-%d %H:%M:%S", 0),
-                      "1970-01-01 00:00:00");
-    BOOST_CHECK_EQUAL(DateTimeStrFormat("%Y-%m-%d %H:%M:%S", 0x7FFFFFFF),
-                      "2038-01-19 03:14:07");
-    BOOST_CHECK_EQUAL(DateTimeStrFormat("%Y-%m-%d %H:%M:%S", 1317425777),
-                      "2011-09-30 23:36:17");
-    BOOST_CHECK_EQUAL(DateTimeStrFormat("%Y-%m-%dT%H:%M:%SZ", 1317425777),
-                      "2011-09-30T23:36:17Z");
-    BOOST_CHECK_EQUAL(DateTimeStrFormat("%H:%M:%SZ", 1317425777), "23:36:17Z");
-    BOOST_CHECK_EQUAL(DateTimeStrFormat("%Y-%m-%d %H:%M", 1317425777),
-                      "2011-09-30 23:36");
-    BOOST_CHECK_EQUAL(
-        DateTimeStrFormat("%a, %d %b %Y %H:%M:%S +0000", 1317425777),
-        "Fri, 30 Sep 2011 23:36:17 +0000");
-}
-
 BOOST_AUTO_TEST_CASE(util_FormatISO8601DateTime) {
     BOOST_CHECK_EQUAL(FormatISO8601DateTime(1317425777),
                       "2011-09-30T23:36:17Z");
diff --git a/src/utiltime.h b/src/utiltime.h
--- a/src/utiltime.h
+++ b/src/utiltime.h
@@ -32,8 +32,6 @@
  * ISO 8601 formatting is preferred. Use the FormatISO8601{DateTime,Date,Time}
  * helper functions if possible.
  */
-std::string DateTimeStrFormat(const char *pszFormat, int64_t nTime);
-
 std::string FormatISO8601DateTime(int64_t nTime);
 std::string FormatISO8601Date(int64_t nTime);
 std::string FormatISO8601Time(int64_t nTime);
diff --git a/src/utiltime.cpp b/src/utiltime.cpp
--- a/src/utiltime.cpp
+++ b/src/utiltime.cpp
@@ -12,7 +12,10 @@
 #include <boost/date_time/posix_time/posix_time.hpp>
 #include <boost/thread.hpp>
 
+#include <tinyformat.h>
+
 #include <atomic>
+#include <ctime>
 
 //!< For unit testing
 static std::atomic<int64_t> nMockTime(0);
@@ -60,24 +63,38 @@
     boost::this_thread::sleep_for(boost::chrono::milliseconds(n));
 }
 
-std::string DateTimeStrFormat(const char *pszFormat, int64_t nTime) {
-    static std::locale classic(std::locale::classic());
-    // std::locale takes ownership of the pointer
-    std::locale loc(classic, new boost::posix_time::time_facet(pszFormat));
-    std::stringstream ss;
-    ss.imbue(loc);
-    ss << boost::posix_time::from_time_t(nTime);
-    return ss.str();
-}
-
 std::string FormatISO8601DateTime(int64_t nTime) {
-    return DateTimeStrFormat("%Y-%m-%dT%H:%M:%SZ", nTime);
+    struct tm ts;
+    time_t time_val = nTime;
+#ifdef _MSC_VER
+    gmtime_s(&ts, &time_val);
+#else
+    gmtime_r(&time_val, &ts);
+#endif
+    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 FormatISO8601Date(int64_t nTime) {
-    return DateTimeStrFormat("%Y-%m-%d", nTime);
+    struct tm ts;
+    time_t time_val = nTime;
+#ifdef _MSC_VER
+    gmtime_s(&ts, &time_val);
+#else
+    gmtime_r(&time_val, &ts);
+#endif
+    return strprintf("%04i-%02i-%02i", ts.tm_year + 1900, ts.tm_mon + 1,
+                     ts.tm_mday);
 }
 
 std::string FormatISO8601Time(int64_t nTime) {
-    return DateTimeStrFormat("%H:%M:%SZ", nTime);
+    struct tm ts;
+    time_t time_val = nTime;
+#ifdef _MSC_VER
+    gmtime_s(&ts, &time_val);
+#else
+    gmtime_r(&time_val, &ts);
+#endif
+    return strprintf("%02i:%02i:%02iZ", ts.tm_hour, ts.tm_min, ts.tm_sec);
 }