diff --git a/src/timers.cc b/src/timers.cc
index 7613ff92..221b594a 100644
--- a/src/timers.cc
+++ b/src/timers.cc
@@ -178,40 +178,64 @@ double ThreadCPUUsage() {
 #endif
 }
 
-namespace {
-
-std::string DateTimeString(bool local) {
+std::string LocalDateTimeString() {
+  // Write the local time in RFC3339 format yyyy-mm-ddTHH:MM:SS+/-HH:MM.
   typedef std::chrono::system_clock Clock;
   std::time_t now = Clock::to_time_t(Clock::now());
-  const std::size_t kStorageSize = 128;
-  char storage[kStorageSize];
-  std::size_t written;
+  const std::size_t kTzOffsetLen = 6;
+  const std::size_t kTimestampLen = 19;
+
+  std::size_t tz_len;
+  std::size_t timestamp_len;
+  long int offset_minutes;
+  char tz_offset_sign = '+';
+  char tz_offset[kTzOffsetLen + 1];
+  char storage[kTimestampLen + kTzOffsetLen + 1];
 
-  if (local) {
 #if defined(BENCHMARK_OS_WINDOWS)
-    written =
-        std::strftime(storage, sizeof(storage), "%x %X", ::localtime(&now));
+  std::tm *timeinfo_p = ::localtime(&now);
 #else
-    std::tm timeinfo;
-    ::localtime_r(&now, &timeinfo);
-    written = std::strftime(storage, sizeof(storage), "%F %T", &timeinfo);
+  std::tm timeinfo;
+  std::tm *timeinfo_p = &timeinfo;
+  ::localtime_r(&now, &timeinfo);
 #endif
+
+  tz_len = std::strftime(tz_offset, sizeof(tz_offset), "%z", timeinfo_p);
+
+  if (tz_len < kTzOffsetLen && tz_len > 1) {
+    // Timezone offset was written. strftime writes offset as +HHMM or -HHMM,
+    // RFC3339 specifies an offset as +HH:MM or -HH:MM. To convert, we parse
+    // the offset as an integer, then reprint it to a string.
+
+    offset_minutes = ::strtol(tz_offset, NULL, 10);
+    if (offset_minutes < 0) {
+      offset_minutes *= -1;
+      tz_offset_sign = '-';
+    }
+    tz_len = ::sprintf(tz_offset, "%c%02li:%02li", tz_offset_sign,
+        offset_minutes / 100, offset_minutes % 100);
+    CHECK(tz_len == 6);
+    ((void)tz_len); // Prevent unused variable warning in optimized build.
   } else {
+    // Unknown offset. RFC3339 specifies that unknown local offsets should be
+    // written as UTC time with -00:00 timezone.
 #if defined(BENCHMARK_OS_WINDOWS)
-    written = std::strftime(storage, sizeof(storage), "%x %X", ::gmtime(&now));
+    // Potential race condition if another thread calls localtime or gmtime.
+    timeinfo_p = ::gmtime(&now);
 #else
-    std::tm timeinfo;
     ::gmtime_r(&now, &timeinfo);
-    written = std::strftime(storage, sizeof(storage), "%F %T", &timeinfo);
 #endif
+
+    strncpy(tz_offset, "-00:00", kTzOffsetLen + 1);
   }
-  CHECK(written < kStorageSize);
-  ((void)written);  // prevent unused variable in optimized mode.
+
+  timestamp_len = std::strftime(storage, sizeof(storage), "%Y-%m-%dT%H:%M:%S",
+      timeinfo_p);
+  CHECK(timestamp_len == kTimestampLen);
+  ((void)timestamp_len); // Prevent unused variable warning in optimized build.
+
+  std::strncat(storage, tz_offset, kTzOffsetLen + 1);
   return std::string(storage);
 }
 
-}  // end namespace
-
-std::string LocalDateTimeString() { return DateTimeString(true); }
-
 }  // end namespace benchmark
diff --git a/test/reporter_output_test.cc b/test/reporter_output_test.cc
index 1a96b5f0..d806a4e8 100644
--- a/test/reporter_output_test.cc
+++ b/test/reporter_output_test.cc
@@ -15,7 +15,7 @@ ADD_CASES(TC_ConsoleOut, {{"^[-]+$", MR_Next},
 static int AddContextCases() {
   AddCases(TC_ConsoleErr,
            {
-               {"%int[-/]%int[-/]%int %int:%int:%int$", MR_Default},
+               {"^%int-%int-%intT%int:%int:%int[-+]%int:%int$", MR_Default},
                {"Running .*/reporter_output_test(\\.exe)?$", MR_Next},
                {"Run on \\(%int X %float MHz CPU s?\\)", MR_Next},
            });