Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -25,6 +25,12 @@
 option(BUILD_QCH "Build API documentation in QCH format (for e.g. Qt Assistant, Qt Creator & KDevelop)" OFF)
 add_feature_info(QCH ${BUILD_QCH} "API documentation in QCH format (for e.g. Qt Assistant, Qt Creator & KDevelop)")
 
+# TODO KF6: remove
+option(KWINDOWSYSTEM_NO_WIDGETS "Disable deprecated API including QWidget usage, so that KWindowSystem does not link to QtWidgets. Warning: this is binary and source incompatible.")
+if (KWINDOWSYSTEM_NO_WIDGETS)
+    add_compile_definitions(KWINDOWSYSTEM_NO_DEPRECATED)
+endif()
+
 ecm_setup_version(PROJECT VARIABLE_PREFIX KWINDOWSYSTEM
                         VERSION_HEADER "${CMAKE_CURRENT_BINARY_DIR}/kwindowsystem_version.h"
                         PACKAGE_VERSION_FILE "${CMAKE_CURRENT_BINARY_DIR}/KF5WindowSystemConfigVersion.cmake"
Index: src/CMakeLists.txt
===================================================================
--- src/CMakeLists.txt
+++ src/CMakeLists.txt
@@ -75,9 +75,12 @@
 target_include_directories(KF5WindowSystem INTERFACE "$<INSTALL_INTERFACE:${KDE_INSTALL_INCLUDEDIR_KF5}/KWindowSystem>")
 
 target_link_libraries(KF5WindowSystem
-    PUBLIC Qt5::Widgets
+    PUBLIC Qt5::Gui
     PRIVATE ${platformLinkLibraries}
 )
+if(NOT KWINDOWSYSTEM_NO_WIDGETS)
+    target_link_libraries(KF5WindowSystem PUBLIC Qt5::Widgets)
+endif()
 
 if(KWINDOWSYSTEM_HAVE_X11)
     # we install kkeyserver_x11.h which needs the X11 headers available
@@ -139,7 +142,7 @@
             ${CMAKE_CURRENT_SOURCE_DIR}
         MD_MAINPAGE "${CMAKE_SOURCE_DIR}/README.md"
         LINK_QCHS
-            Qt5Widgets_QCH
+            Qt5Gui_QCH
         BLANK_MACROS
             KWINDOWSYSTEM_EXPORT
             KWINDOWSYSTEM_DEPRECATED