diff --git a/autotests/testicalformat.h b/autotests/testicalformat.h
--- a/autotests/testicalformat.h
+++ b/autotests/testicalformat.h
@@ -33,6 +33,8 @@
     void testVolatileProperties();
     void testCuType();
     void testAlarm();
+    void testDateTime_data();
+    void testDateTime();
 };
 
 #endif
diff --git a/autotests/testicalformat.cpp b/autotests/testicalformat.cpp
--- a/autotests/testicalformat.cpp
+++ b/autotests/testicalformat.cpp
@@ -170,3 +170,48 @@
     Alarm::Ptr alarm2 = event2->alarms()[0];
     QCOMPARE(*alarm, *alarm2);
 }
+
+void ICalFormatTest::testDateTime_data()
+{
+    QTest::addColumn<QByteArray>("dtStartData");
+    QTest::addColumn<QDateTime>("dtStart");
+
+    QTest::newRow("clock time")
+        << QByteArray("DTSTART:20191113T130000")
+        << QDateTime(QDate(2019, 11, 13), QTime(13, 00), Qt::LocalTime);
+    QTest::newRow("date")
+        << QByteArray("DTSTART;VALUE=DATE:20191113")
+        << QDateTime(QDate(2019, 11, 13));
+    QTest::newRow("UTC time")
+        << QByteArray("DTSTART:20191113T130000Z")
+        << QDateTime(QDate(2019, 11, 13), QTime(13, 00), Qt::UTC);
+    QTest::newRow("time zone time")
+        << QByteArray("DTSTART;TZID=Europe/Paris:20191113T130000")
+        << QDateTime(QDate(2019, 11, 13), QTime(13, 00), QTimeZone("Europe/Paris"));
+}
+
+void ICalFormatTest::testDateTime()
+{
+    QFETCH(QByteArray, dtStartData);
+    QFETCH(QDateTime, dtStart);
+
+    // test fromString(QString)
+    const QByteArray serializedCalendar
+        = "BEGIN:VCALENDAR\nPRODID:-//K Desktop Environment//NONSGML libkcal 3.2//EN\nVERSION:2.0\nBEGIN:VEVENT\nUID:12345\n"
+          + dtStartData
+          + "\nEND:VEVENT\nEND:VCALENDAR";
+
+    ICalFormat format;
+    Incidence::Ptr event = format.fromString(QString::fromUtf8(serializedCalendar));
+    QVERIFY(event);
+    QCOMPARE(dtStart, event->dtStart());
+
+    const QByteArray output = format.toRawString(event);
+    const QList<QByteArray> lines = output.split('\n');
+    for (const QByteArray &line: lines) {
+        if (line.startsWith(QByteArray("DTSTART"))) {
+            QCOMPARE(line.chopped(1), dtStartData);
+            break;
+        }
+    }
+}
diff --git a/src/icalformat_p.cpp b/src/icalformat_p.cpp
--- a/src/icalformat_p.cpp
+++ b/src/icalformat_p.cpp
@@ -2369,11 +2369,13 @@
     t.zone = nullptr;   // zone is NOT set
 #if defined(USE_ICAL_3)
     if (datetime.timeSpec() == Qt::UTC ||
+        (datetime.timeSpec() == Qt::TimeZone && datetime.timeZone() == QTimeZone::utc()) ||
         (datetime.timeSpec() == Qt::OffsetFromUTC && datetime.offsetFromUtc() == 0)) {
         t = icaltime_convert_to_zone(t, icaltimezone_get_utc_timezone());
     }
 #else
     t.is_utc = datetime.timeSpec() == Qt::UTC ||
+        (datetime.timeSpec() == Qt::TimeZone && datetime.timeZone() == QTimeZone::utc()) ||
         (datetime.timeSpec() == Qt::OffsetFromUTC && datetime.offsetFromUtc() == 0);
 #endif
     return t;
@@ -2445,9 +2447,9 @@
 
     QTimeZone qtz;
 #if defined(USE_ICAL_3)
-    if (!icaltime_is_utc(t)) {
+    if (!icaltime_is_utc(t) && dt.timeSpec() == Qt::TimeZone) {
 #else
-    if (!t.is_utc) {
+    if (!t.is_utc && dt.timeSpec() == Qt::TimeZone) {
 #endif
         qtz = dt.timeZone();
     }
@@ -2496,21 +2498,21 @@
             // First try to get the timezone from cache
             timeZone = tzCache->tzForTime(QDateTime({ t.year, t.month, t.day }, {}), tzid);
         }
-        if (!timeZone.isValid()) {
+        if (!timeZone.isValid() && !tzid.isEmpty()) {
             // Fallback to trying to match against Qt timezone
             timeZone = QTimeZone(tzid);
         }
-        if (!timeZone.isValid()) {
-            // Finally, give up and assume local timezone
-            timeZone = QTimeZone::systemTimeZone();
-        }
+        // If Time zone is still invalid, we will use LocalTime as TimeSpec.
+    }
+    QTime resultTime;
+    if (!t.is_date) {
+        resultTime = QTime(t.hour, t.minute, t.second);
     }
     QDateTime result;
-    if (t.is_date) {
-        result = QDateTime(QDate(t.year, t.month, t.day), {}, timeZone);
+    if (timeZone.isValid()) {
+        result = QDateTime(QDate(t.year, t.month, t.day), resultTime, timeZone);
     } else {
-        result = QDateTime(QDate(t.year, t.month, t.day),
-                           QTime(t.hour, t.minute, t.second), timeZone);
+        result = QDateTime(QDate(t.year, t.month, t.day), resultTime);
     }
     return utc ? result.toUTC() : result;
 }
diff --git a/src/icaltimezones.cpp b/src/icaltimezones.cpp
--- a/src/icaltimezones.cpp
+++ b/src/icaltimezones.cpp
@@ -138,7 +138,7 @@
 
     const ICalTimeZone tz = mCache.value(tzid);
     if (!tz.qZone.isValid()) {
-        return QTimeZone::systemTimeZone();
+        return QTimeZone();
     }
 
     // If the matched timezone is one of the UTC offset timezones, we need to make