diff --git a/pyconfig.h.in b/pyconfig.h.in
index 2d1fd48..efe732f 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -95,6 +95,9 @@
 /* define to 1 if your sem_getvalue is broken. */
 #undef HAVE_BROKEN_SEM_GETVALUE
 
+/* Define if `unsetenv` does not return an int. */
+#undef HAVE_BROKEN_UNSETENV
+
 /* Define this if you have the type _Bool. */
 #undef HAVE_C99_BOOL