diff --git a/cmake/QtModuleHelpers.cmake b/cmake/QtModuleHelpers.cmake
index 792821777e5..6f85384d5db 100644
--- a/cmake/QtModuleHelpers.cmake
+++ b/cmake/QtModuleHelpers.cmake
@@ -1238,10 +1238,13 @@ function(qt_internal_collect_module_headers out_var target)
     get_target_property(target_type ${target} TYPE)
     if(target_type STREQUAL "INTERFACE_LIBRARY")
         set(source_dir "${CMAKE_CURRENT_SOURCE_DIR}")
+        set(binary_dir "${CMAKE_CURRENT_BINARY_DIR}")
     else()
         get_target_property(source_dir ${target} SOURCE_DIR)
+        get_target_property(binary_dir ${target} BINARY_DIR)
     endif()
     get_filename_component(source_dir "${source_dir}" ABSOLUTE)
+    get_filename_component(binary_dir "${binary_dir}" ABSOLUTE)
 
     get_target_property(is_3rdparty_library ${target} _qt_module_is_3rdparty_header_library)
 
@@ -1285,7 +1288,14 @@ function(qt_internal_collect_module_headers out_var target)
                 "\nCondition:\n    ${condition_string}")
         endif()
 
-        if(file_path MATCHES "3rdparty/.+" AND NOT is_3rdparty_library)
+        if(is_outside_module_source_dir)
+            set(base_dir "${binary_dir}")
+        else()
+            set(base_dir "${source_dir}")
+        endif()
+
+        file(RELATIVE_PATH file_path_rel "${base_dir}" "${file_path}")
+        if(file_path_rel MATCHES "3rdparty/.+" AND NOT is_3rdparty_library)
             set(is_3rdparty_header TRUE)
         else()
             set(is_3rdparty_header FALSE)