diff --git a/src/corelib/time/qdatetime.cpp b/src/corelib/time/qdatetime.cpp
index 6bf29bc0d6..98a1437f8d 100644
--- a/src/corelib/time/qdatetime.cpp
+++ b/src/corelib/time/qdatetime.cpp
@@ -3180,9 +3180,8 @@ static void setTimeSpec(QDateTimeData &d, Qt::TimeSpec spec, int offsetSeconds)
 static void setDateTime(QDateTimeData &d, QDate date, QTime time)
 {
     // If the date is valid and the time is not we set time to 00:00:00
-    QTime useTime = time;
-    if (!useTime.isValid() && date.isValid())
-        useTime = QTime::fromMSecsSinceStartOfDay(0);
+    if (!time.isValid() && date.isValid())
+        time = QTime::fromMSecsSinceStartOfDay(0);
 
     QDateTimePrivate::StatusFlags newStatus = { };
 
@@ -3195,8 +3194,8 @@ static void setDateTime(QDateTimeData &d, QDate date, QTime time)
 
     // Set time value and status
     int ds = 0;
-    if (useTime.isValid()) {
-        ds = useTime.msecsSinceStartOfDay();
+    if (time.isValid()) {
+        ds = time.msecsSinceStartOfDay();
         newStatus |= QDateTimePrivate::ValidTime;
     }
     Q_ASSERT(ds < MSECS_PER_DAY);
diff --git a/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp b/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
index 844dead504..b8b5319ecb 100644
--- a/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
+++ b/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2021 The Qt Company Ltd.
+** Copyright (C) 2022 The Qt Company Ltd.
 ** Copyright (C) 2016 Intel Corporation.
 ** Contact: https://www.qt.io/licensing/
 **
@@ -341,14 +341,26 @@ void tst_QDateTime::isNull()
     dt1.setTime(QTime());
     QVERIFY(dt1.isNull());
     dt1.setTimeSpec(Qt::UTC);
-    QVERIFY(dt1.isNull());   // maybe it should return false?
+    QVERIFY(dt1.isNull());
 
+    dt1.setTime(QTime(12, 34, 56));
+    QVERIFY(!dt1.isNull());
+    dt1.setTime(QTime()); // Date still invalid, so this really clears time.
+    QVERIFY(dt1.isNull());
     dt1.setDate(QDate(2004, 1, 2));
     QVERIFY(!dt1.isNull());
     dt1.setTime(QTime(12, 34, 56));
     QVERIFY(!dt1.isNull());
-    dt1.setTime(QTime());
+    dt1.setTime(QTime()); // Actually sets time to QTime(0, 0), as date is still valid.
     QVERIFY(!dt1.isNull());
+    dt1.setDate(QDate()); // Time remains valid
+    QVERIFY(!dt1.isNull());
+    dt1.setTime(QTime()); // Now really sets time invalid, too
+    QVERIFY(dt1.isNull());
+
+    // Either date or time non-null => date-time isn't null:
+    QVERIFY(!QDateTime(QDate(), QTime(0, 0)).isNull());
+    QVERIFY(!QDateTime(QDate(2022, 2, 16), QTime()).isNull());
 }
 
 void tst_QDateTime::isValid()
@@ -364,12 +376,21 @@ void tst_QDateTime::isValid()
 
     dt1.setDate(QDate(2004, 1, 2));
     QVERIFY(dt1.isValid());
+    dt1.setTime(QTime()); // Effectively QTime(0, 0)
+    QVERIFY(dt1.isValid());
     dt1.setDate(QDate());
     QVERIFY(!dt1.isValid());
     dt1.setTime(QTime(12, 34, 56));
     QVERIFY(!dt1.isValid());
-    dt1.setTime(QTime());
+    dt1.setTime(QTime()); // Does sets time invalid, as date is invalid
     QVERIFY(!dt1.isValid());
+    dt1.setDate(QDate(2004, 1, 2)); // Kicks time back to QTime(0, 0)
+    QVERIFY(dt1.isValid());
+
+    // Invalid date => invalid date-time:
+    QVERIFY(!QDateTime(QDate(), QTime(0, 0)).isValid());
+    // Invalid time gets replaced with QTime(0, 0) when date is valid:
+    QVERIFY(QDateTime(QDate(2022, 2, 16), QTime()).isValid());
 }
 
 void tst_QDateTime::date()