diff --git a/src/corelib/time/qtimezone.cpp b/src/corelib/time/qtimezone.cpp
index 9ccb0e5f024..5a5cd1dd101 100644
--- a/src/corelib/time/qtimezone.cpp
+++ b/src/corelib/time/qtimezone.cpp
@@ -334,6 +334,9 @@ QTimeZone::QTimeZone() noexcept
 
 QTimeZone::QTimeZone(const QByteArray &ianaId)
 {
+    // If invalid (other than empty), reject immediately:
+    if (!ianaId.isEmpty() && !QTimeZonePrivate::isValidId(ianaId))
+        return;
     // Try and see if it's a CLDR UTC offset ID - just as quick by creating as
     // by looking up.
     d = new QUtcTimeZonePrivate(ianaId);
diff --git a/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp b/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
index 9c505e5baaf..13300cee683 100644
--- a/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
+++ b/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
@@ -1000,6 +1000,9 @@ void tst_QTimeZone::malformed()
     barf = QTimeZone("QtC+09,,MA");
     if (barf.isValid())
         QCOMPARE(barf.offsetFromUtc(now), 0);
+    barf = QTimeZone("UTCC+14:00,-,");
+    if (barf.isValid())
+        QCOMPARE(barf.daylightTimeOffset(now), -14 * 3600);
 }
 
 void tst_QTimeZone::utcTest()