diff --git a/src/corelib/tools/qtimezone.cpp b/src/corelib/tools/qtimezone.cpp
index 445ddeb31de..db6be581ec8 100644
--- a/src/corelib/tools/qtimezone.cpp
+++ b/src/corelib/tools/qtimezone.cpp
@@ -820,8 +820,8 @@ bool QTimeZone::isTimeZoneIdAvailable(const QByteArray &ianaId)
     // IDs as availableTimeZoneIds() may be slow
     if (!QTimeZonePrivate::isValidId(ianaId))
         return false;
-    const QList<QByteArray> tzIds = availableTimeZoneIds();
-    return std::binary_search(tzIds.begin(), tzIds.end(), ianaId);
+    return QUtcTimeZonePrivate().isTimeZoneIdAvailable(ianaId) ||
+           global_tz->backend->isTimeZoneIdAvailable(ianaId);
 }
 
 static QList<QByteArray> set_union(const QList<QByteArray> &l1, const QList<QByteArray> &l2)
diff --git a/src/corelib/tools/qtimezoneprivate.cpp b/src/corelib/tools/qtimezoneprivate.cpp
index 1a5135f1035..2b6c2ea6a55 100644
--- a/src/corelib/tools/qtimezoneprivate.cpp
+++ b/src/corelib/tools/qtimezoneprivate.cpp
@@ -486,6 +486,13 @@ QByteArray QTimeZonePrivate::systemTimeZoneId() const
     return QByteArray();
 }
 
+bool QTimeZonePrivate::isTimeZoneIdAvailable(const QByteArray& ianaId) const
+{
+    // Fall-back implementation, can be made faster in subclasses
+    const QList<QByteArray> tzIds = availableTimeZoneIds();
+    return std::binary_search(tzIds.begin(), tzIds.end(), ianaId);
+}
+
 QList<QByteArray> QTimeZonePrivate::availableTimeZoneIds() const
 {
     return QList<QByteArray>();
@@ -864,6 +871,17 @@ QByteArray QUtcTimeZonePrivate::systemTimeZoneId() const
     return utcQByteArray();
 }
 
+bool QUtcTimeZonePrivate::isTimeZoneIdAvailable(const QByteArray &ianaId) const
+{
+    for (int i = 0; i < utcDataTableSize; ++i) {
+        const QUtcData *data = utcData(i);
+        if (utcId(data) == ianaId) {
+            return true;
+        }
+    }
+    return false;
+}
+
 QList<QByteArray> QUtcTimeZonePrivate::availableTimeZoneIds() const
 {
     QList<QByteArray> result;
diff --git a/src/corelib/tools/qtimezoneprivate_p.h b/src/corelib/tools/qtimezoneprivate_p.h
index 4d357111f28..c9a57262166 100644
--- a/src/corelib/tools/qtimezoneprivate_p.h
+++ b/src/corelib/tools/qtimezoneprivate_p.h
@@ -128,6 +128,7 @@ public:
 
     virtual QByteArray systemTimeZoneId() const;
 
+    virtual bool isTimeZoneIdAvailable(const QByteArray &ianaId) const;
     virtual QList<QByteArray> availableTimeZoneIds() const;
     virtual QList<QByteArray> availableTimeZoneIds(QLocale::Country country) const;
     virtual QList<QByteArray> availableTimeZoneIds(int utcOffset) const;
@@ -204,6 +205,7 @@ public:
 
     QByteArray systemTimeZoneId() const override;
 
+    bool isTimeZoneIdAvailable(const QByteArray &ianaId) const override;
     QList<QByteArray> availableTimeZoneIds() const override;
     QList<QByteArray> availableTimeZoneIds(QLocale::Country country) const override;
     QList<QByteArray> availableTimeZoneIds(int utcOffset) const override;
@@ -323,6 +325,7 @@ public:
 
     QByteArray systemTimeZoneId() const override;
 
+    bool isTimeZoneIdAvailable(const QByteArray &ianaId) const override;
     QList<QByteArray> availableTimeZoneIds() const override;
     QList<QByteArray> availableTimeZoneIds(QLocale::Country country) const override;
 
diff --git a/src/corelib/tools/qtimezoneprivate_tz.cpp b/src/corelib/tools/qtimezoneprivate_tz.cpp
index 6a5df6272a5..f1735a80e79 100644
--- a/src/corelib/tools/qtimezoneprivate_tz.cpp
+++ b/src/corelib/tools/qtimezoneprivate_tz.cpp
@@ -1098,6 +1098,11 @@ QByteArray QTzTimeZonePrivate::systemTimeZoneId() const
     return ianaId;
 }
 
+bool QTzTimeZonePrivate::isTimeZoneIdAvailable(const QByteArray &ianaId) const
+{
+    return tzZones->contains(ianaId);
+}
+
 QList<QByteArray> QTzTimeZonePrivate::availableTimeZoneIds() const
 {
     QList<QByteArray> result = tzZones->keys();
diff --git a/tests/benchmarks/corelib/tools/qtimezone/main.cpp b/tests/benchmarks/corelib/tools/qtimezone/main.cpp
new file mode 100644
index 00000000000..65455a72619
--- /dev/null
+++ b/tests/benchmarks/corelib/tools/qtimezone/main.cpp
@@ -0,0 +1,52 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 Klaralvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author David Faure <david.faure@kdab.com>
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QTimeZone>
+#include <QTest>
+#include <qdebug.h>
+
+class tst_QTimeZone : public QObject
+{
+    Q_OBJECT
+
+private Q_SLOTS:
+    void isTimeZoneIdAvailable();
+};
+
+void tst_QTimeZone::isTimeZoneIdAvailable()
+{
+    const QList<QByteArray> available = QTimeZone::availableTimeZoneIds();
+    QBENCHMARK {
+        for (const QByteArray &id : available)
+            QVERIFY(QTimeZone::isTimeZoneIdAvailable(id));
+    }
+}
+
+QTEST_MAIN(tst_QTimeZone)
+
+#include "main.moc"
diff --git a/tests/benchmarks/corelib/tools/qtimezone/qtimezone.pro b/tests/benchmarks/corelib/tools/qtimezone/qtimezone.pro
new file mode 100644
index 00000000000..d0531b568bf
--- /dev/null
+++ b/tests/benchmarks/corelib/tools/qtimezone/qtimezone.pro
@@ -0,0 +1,4 @@
+TARGET = tst_bench_qtimezone
+QT = core testlib
+
+SOURCES += main.cpp
diff --git a/tests/benchmarks/corelib/tools/tools.pro b/tests/benchmarks/corelib/tools/tools.pro
index af9b7d241d5..ca9c0a6f898 100644
--- a/tests/benchmarks/corelib/tools/tools.pro
+++ b/tests/benchmarks/corelib/tools/tools.pro
@@ -15,6 +15,7 @@ SUBDIRS = \
         qstring \
         qstringbuilder \
         qstringlist \
+        qtimezone \
         qvector \
         qalgorithms