diff -rupN --no-dereference PyQt5-5.15.0/configure.py PyQt5-5.15.0-new/configure.py
--- PyQt5-5.15.0/configure.py	2020-05-31 14:10:54.334553000 +0200
+++ PyQt5-5.15.0-new/configure.py	2020-08-18 15:47:11.505131208 +0200
@@ -2666,7 +2666,7 @@ def generate_sip_module_code(target_conf
                 os.path.join('QtCore', 'qpycore_post_init.cpp'))
 
         for line in in_f:
-            line = line.replace('@@PYQT_SIP_FLAGS@@', ' '.join(sip_flags))
+            line = line.replace('@@PYQT_SIP_FLAGS@@', ' '.join(sip_flags).replace("WS_X11", "WS_WIN"))
             out_f.write(line)
 
         in_f.close()