--- a/Modules/posixmodule.c	2021-08-02 20:53:59.000000000 +0100
+++ b/Modules/posixmodule.c	2021-08-21 12:06:16.897465398 +0100
@@ -15384,6 +15384,9 @@
 #ifdef HAVE_EVENTFD
     if (PyModule_AddIntMacro(m, EFD_CLOEXEC)) return -1;
     if (PyModule_AddIntMacro(m, EFD_NONBLOCK)) return -1;
+#  ifndef EFD_SEMAPHORE
+#    define EFD_SEMAPHORE (1 << 0)
+#  endif
     if (PyModule_AddIntMacro(m, EFD_SEMAPHORE)) return -1;
 #endif