diff --git a/startkde/startplasma.cpp b/startkde/startplasma.cpp
--- a/startkde/startplasma.cpp
+++ b/startkde/startplasma.cpp
@@ -185,12 +185,20 @@
     }
     sourceFiles(scripts);
 
-    // Make sure that the KDE prefix is first in XDG_DATA_DIRS and that it's set at all.
-    // The spec allows XDG_DATA_DIRS to be not set, but X session startup scripts tend
-    // to set it to a list of paths *not* including the KDE prefix if it's not /usr or
-    // /usr/local.
-    if (!qEnvironmentVariableIsSet("XDG_DATA_DIRS")) {
-        qputenv("XDG_DATA_DIRS", KDE_INSTALL_FULL_DATAROOTDIR ":/usr/share:/usr/local/share");
+    // To ensure the proper resources are available, the data root dir
+    // needs to be available in the XDG_DATA_DIRS variable, with
+    // the right preference.
+    QString xdgDataDirsValue;
+    if (qEnvironmentVariableIsSet("XDG_DATA_DIRS")) {
+        xdgDataDirsValue = QString::fromLocal8Bit(qgetenv("XDG_DATA_DIRS"));
+    } else {
+        xdgDataDirsValue = QLatin1String("/usr/local/share:/usr/share");
+    }
+    const QString kdeInstallFullDataRootDir = QStringLiteral(KDE_INSTALL_FULL_DATAROOTDIR);
+    QVector<QStringRef> xdgDataDirs = xdgDataDirsValue.splitRef(QLatin1Char(':'));
+    if (!xdgDataDirs.contains(QStringRef(&kdeInstallFullDataRootDir))) {
+        QString xdgDataDirsNewValue = kdeInstallFullDataRootDir + QLatin1Char(':') + xdgDataDirsValue;
+        qputenv("XDG_DATA_DIRS", xdgDataDirsNewValue.toLocal8Bit());
     }
 }