diff --git a/cmake/QtHeadersClean.cmake b/cmake/QtHeadersClean.cmake
index 8abb34ff9e5..b6706f571db 100644
--- a/cmake/QtHeadersClean.cmake
+++ b/cmake/QtHeadersClean.cmake
@@ -144,8 +144,8 @@ function(qt_internal_add_headers_clean_target
             endif()
         endif()
 
-        # Use strict mode C++17, with no GNU extensions (see -pedantic-errors above).
-        list(APPEND hcleanFLAGS -std=c++17)
+        # Use strict mode C++20, with no GNU extensions (see -pedantic-errors above).
+        list(APPEND hcleanFLAGS -std=c++2a)
 
         set(cxx_flags ${CMAKE_CXX_FLAGS})