diff --git a/src/corelib/Qt6CoreMacros.cmake b/src/corelib/Qt6CoreMacros.cmake
index dc5afae6c5..206ce8f21e 100644
--- a/src/corelib/Qt6CoreMacros.cmake
+++ b/src/corelib/Qt6CoreMacros.cmake
@@ -1744,6 +1744,7 @@ function(_qt_internal_expose_deferred_files_to_ide target)
         list(APPEND new_sources_real ${realf})
     endforeach()
 
+    set(filtered_new_sources "")
     get_target_property(target_source_dir ${target} SOURCE_DIR)
     get_filename_component(target_source_dir "${target_source_dir}" REALPATH)
     get_target_property(existing_sources ${target} SOURCES)
@@ -1754,25 +1755,28 @@ function(_qt_internal_expose_deferred_files_to_ide target)
             get_filename_component(realf "${f}" REALPATH BASE_DIR ${target_source_dir})
             list(APPEND existing_sources_real ${realf})
         endforeach()
-        list(REMOVE_ITEM new_sources_real ${existing_sources_real})
+
+        list(LENGTH new_sources max_i)
+        math(EXPR max_i "${max_i} - 1")
+        foreach(i RANGE 0 ${max_i})
+            list(GET new_sources_real ${i} realf)
+            if(NOT realf IN_LIST existing_sources_real)
+                list(GET new_sources ${i} f)
+                list(APPEND filtered_new_sources ${f})
+            endif()
+        endforeach()
     endif()
-    if("${new_sources_real}" STREQUAL "")
+    if("${filtered_new_sources}" STREQUAL "")
         return()
     endif()
-    # Need to convert real paths back to relative paths because the use of absolute paths for these
-    # files causes invalid generation of build.ninja on Windows platforms.
-    set(new_sources "")
-    foreach(realf IN LISTS new_sources_real)
-        file(RELATIVE_PATH f "${target_source_dir}" "${realf}")
-        list(APPEND new_sources "${f}")
-    endforeach()
 
-    target_sources(${target} PRIVATE ${new_sources})
+    target_sources(${target} PRIVATE ${filtered_new_sources})
     set(scope_args)
     if(CMAKE_VERSION VERSION_GREATER_EQUAL "3.18")
         set(scope_args TARGET_DIRECTORY "${target}")
     endif()
-    set_source_files_properties(${new_sources} ${scope_args} PROPERTIES HEADER_FILE_ONLY ON)
+    set_source_files_properties(${filtered_new_sources}
+        ${scope_args} PROPERTIES HEADER_FILE_ONLY ON)
 endfunction()
 
 #