diff --git a/startkde/config-startplasma.h.cmake b/startkde/config-startplasma.h.cmake
--- a/startkde/config-startplasma.h.cmake
+++ b/startkde/config-startplasma.h.cmake
@@ -3,6 +3,7 @@
 
 #define CMAKE_INSTALL_FULL_BINDIR "@CMAKE_INSTALL_FULL_BINDIR@"
 #define KDE_INSTALL_FULL_DATAROOTDIR "@KDE_INSTALL_FULL_DATAROOTDIR@"
+#define KDE_INSTALL_FULL_CONFDIR "@KDE_INSTALL_FULL_CONFDIR@"
 #define CMAKE_INSTALL_FULL_LIBEXECDIR "@CMAKE_INSTALL_FULL_LIBEXECDIR@"
 #define CMAKE_INSTALL_FULL_LIBEXECDIR_KF5 "@CMAKE_INSTALL_FULL_LIBEXECDIR_KF5@"
 #define KWIN_WAYLAND_BIN_PATH "@KWIN_WAYLAND_BIN_PATH@"
diff --git a/startkde/startplasma.cpp b/startkde/startplasma.cpp
--- a/startkde/startplasma.cpp
+++ b/startkde/startplasma.cpp
@@ -192,6 +192,10 @@
     if (!qEnvironmentVariableIsSet("XDG_DATA_DIRS")) {
         qputenv("XDG_DATA_DIRS", KDE_INSTALL_FULL_DATAROOTDIR ":/usr/share:/usr/local/share");
     }
+    // Additionally also set default value for XDG_CONFIG_DIRS.
+    if (!qEnvironmentVariableIsSet("XDG_CONFIG_DIRS")) {
+        qputenv("XDG_CONFIG_DIRS", KDE_INSTALL_FULL_CONFDIR ":/etc/xdg:/usr/local/etc/xdg");
+    }
 }