Index: autotests/CMakeLists.txt
===================================================================
--- autotests/CMakeLists.txt
+++ autotests/CMakeLists.txt
@@ -17,3 +17,13 @@
   kiconloader_benchmark
   kicontheme_unittest
 )
+
+### Test for RCC loading
+
+get_target_property(QT_RCC_EXECUTABLE Qt5::rcc LOCATION)
+add_custom_command(OUTPUT icontheme.rcc
+   COMMAND ${QT_RCC_EXECUTABLE} --binary -o icontheme.rcc ${CMAKE_CURRENT_SOURCE_DIR}/icontheme.qrc
+       DEPENDS icontheme.qrc
+)
+ecm_add_test(kiconloader_rcctest.cpp LINK_LIBRARIES Qt5::Test KF5::IconThemes KF5::WidgetsAddons KF5::ConfigCore)
+add_custom_target(rcctest-rcc ALL DEPENDS icontheme.rcc) # a custom target that is always built
Index: autotests/icontheme.qrc
===================================================================
--- /dev/null
+++ autotests/icontheme.qrc
@@ -0,0 +1,6 @@
+<!DOCTYPE RCC><RCC version="1.0">
+<qresource>
+    <file alias="/index.theme">tiny.theme</file>
+    <file alias="/22x22/appsNoContext/someiconintheme.png">test-22x22.png</file>
+</qresource>
+</RCC>
Index: autotests/kiconloader_rcctest.cpp
===================================================================
--- /dev/null
+++ autotests/kiconloader_rcctest.cpp
@@ -0,0 +1,86 @@
+/* This file is part of the KDE libraries
+    Copyright 2015 Christoph Cullmann <cullmann@kde.org>
+    Copyright 2016 David Faure <faure@kde.org>
+
+    This library is free software; you can redistribute it and/or
+    modify it under the terms of the GNU Library General Public
+    License as published by the Free Software Foundation; either
+    version 2 of the License, or (at your option) any later version.
+
+    This library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+    Library General Public License for more details.
+
+    You should have received a copy of the GNU Library General Public License
+    along with this library; see the file COPYING.LIB.  If not, write to
+    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+    Boston, MA 02110-1301, USA.
+*/
+
+#include <kiconloader.h>
+#include <kicontheme.h>
+
+#include <QStandardPaths>
+#include <QPixmap>
+#include <QTest>
+
+#include <KSharedConfig>
+#include <KConfigGroup>
+
+// Install icontheme.rcc where KIconThemes will find it.
+// This must be done before QCoreApplication is even created, given the Q_COREAPP_STARTUP_FUNCTION in kiconthemes
+void earlyInit()
+{
+    QStandardPaths::enableTestMode(true);
+    qputenv("XDG_DATA_DIRS", "/doesnotexist"); // ensure hicolor/oxygen/breeze are not found
+    QFile rcc("icontheme.rcc");
+    Q_ASSERT(rcc.exists());
+    QCoreApplication::setApplicationName("myappname"); // for a fixed location on Unix (appname is empty here otherwise)
+    const QString destDir = QStandardPaths::writableLocation(QStandardPaths::AppDataLocation);
+    QDir().mkpath(destDir);
+    const QString dest = destDir + "/icontheme.rcc";
+    QFile::remove(dest);
+    if (!rcc.copy(dest)) {
+        qWarning() << "Error copying to" << dest;
+    }
+}
+Q_CONSTRUCTOR_FUNCTION(earlyInit)
+
+class KIconLoader_RCCThemeTest : public QObject
+{
+    Q_OBJECT
+
+private Q_SLOTS:
+    void testThemeName()
+    {
+        QCOMPARE(QIcon::themeName(), m_internalThemeName);
+    }
+
+    void testQIconFromTheme()
+    {
+        // load icon with Qt API
+        QVERIFY(!QIcon::fromTheme(QStringLiteral("someiconintheme")).isNull());
+    }
+
+    void testKIconLoader()
+    {
+        // Check that direct usage of KIconLoader (e.g. from KToolBar) works
+        QVERIFY(KIconLoader::global()->theme());
+        QCOMPARE(KIconLoader::global()->theme()->internalName(), m_internalThemeName);
+
+        // load icon with KIconLoader API (unlikely to happen in reality)
+        QString path;
+        KIconLoader::global()->loadIcon(QStringLiteral("someiconintheme"), KIconLoader::Desktop, 22,
+                                    KIconLoader::DefaultState, QStringList(),
+                                    &path);
+        QCOMPARE(path, QString(QStringLiteral(":/icons/") + m_internalThemeName + QStringLiteral("/22x22/appsNoContext/someiconintheme.png")));
+
+    }
+private:
+    const QString m_internalThemeName = "kf5_rcc_theme";
+};
+
+QTEST_MAIN(KIconLoader_RCCThemeTest)
+
+#include "kiconloader_rcctest.moc"
Index: autotests/tiny.theme
===================================================================
--- /dev/null
+++ autotests/tiny.theme
@@ -0,0 +1,38 @@
+[Icon Theme]
+Name=Tiny
+Comment=Tiny icon theme
+Hidden=false
+Directories=22x22/actions,22x22/animations,22x22/apps,22x22/mimetypes,22x22/appsNoContext,22x22/appsNoType,22x22/appsNoContextOrType
+Inherits=hicolor
+FollowsColorScheme=true
+
+[22x22/actions]
+Size=22
+Context=Actions
+Type=Threshold
+
+[22x22/animations]
+Size=22
+Context=Animations
+Type=Threshold
+
+[22x22/apps]
+Size=22
+Context=Applications
+Type=Threshold
+
+[22x22/mimetypes]
+Size=22
+Context=MimeTypes
+Type=Threshold
+
+[22x22/appsNoContext]
+Size=22
+Type=Threshold
+
+[22x22/appsNoType]
+Size=22
+Context=MimeTypes
+
+[22x22/appsNoContextOrType]
+Size=22
Index: src/kicontheme.cpp
===================================================================
--- src/kicontheme.cpp
+++ src/kicontheme.cpp
@@ -25,19 +25,51 @@
 
 #include <qplatformdefs.h>
 
+#include <QCoreApplication>
 #include <QAction>
 #include <QtCore/QMap>
 #include <QtCore/QSet>
 #include <QtCore/QFileInfo>
 #include <QtCore/QDir>
 #include <QDebug>
+#include <QResource>
 
 #include <klocalizedstring.h> // KLocalizedString::localizedFilePath. Need such functionality in, hmm, QLocale? QStandardPaths?
 
 #include <ksharedconfig.h>
 
 #include <kconfiggroup.h>
 
+Q_GLOBAL_STATIC(QString, _themeOverride)
+
+// Support for icon themes in RCC files.
+// The intended use case is standalone apps on Windows / MacOS / etc.
+// For this reason we use AppDataLocation: BINDIR/data on Windows, Resources on OS X
+void initRCCIconTheme()
+{
+    const QString iconThemeRcc = QStandardPaths::locate(QStandardPaths::AppDataLocation, QStringLiteral("icontheme.rcc"));
+    if (!iconThemeRcc.isEmpty()) {
+        const QString iconThemeName = QStringLiteral("kf5_rcc_theme");
+        const QString iconSubdir = QStringLiteral("/icons/") + iconThemeName;
+        if (QResource::registerResource(iconThemeRcc, iconSubdir)) {
+            if (QFileInfo::exists(QLatin1Char(':') + iconSubdir + QStringLiteral("/index.theme"))) {
+                // Tell Qt about the theme
+                // Note that since qtbase commit a8621a3f8, this means the QPA (i.e. KIconLoader) will NOT be used.
+                QIcon::setThemeName(iconThemeName); // Qt looks under :/icons automatically
+                // Tell KIconTheme about the theme, in case KIconLoader is used directly
+                *_themeOverride() = iconThemeName;
+            } else {
+                qWarning() << "No index.theme found in" << iconThemeRcc;
+                QResource::unregisterResource(iconThemeRcc, iconSubdir);
+            }
+        } else {
+            qWarning() << "Invalid rcc file" << iconThemeRcc;
+        }
+    }
+}
+Q_COREAPP_STARTUP_FUNCTION(initRCCIconTheme)
+
+
 class KIconTheme::KIconThemePrivate
 {
 public:
@@ -56,7 +88,6 @@
     QVector<KIconThemeDir *> mDirs;
     bool followsColorScheme : 1;
 };
-Q_GLOBAL_STATIC(QString, _themeOverride)
 Q_GLOBAL_STATIC(QString, _theme)
 Q_GLOBAL_STATIC(QStringList, _theme_list)