diff --git a/lprefix.h b/lprefix.h
index 41939d7..f401c9c 100644
--- a/lprefix.h
+++ b/lprefix.h
@@ -195,12 +195,11 @@ LUAMOD_API int luaopen_compat53_string (lua_State *L) {
 #  endif
 
 /* choose which popen implementation to pick */
-#  if (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 200112L) || \
-      (defined(_XOPEN_SOURCE) && _XOPEN_SOURCE >= 600) || \
-      defined(__APPLE__)
+#  if (!defined(LUA_USE_WINDOWS) && !defined(LUA_USE_POSIX)) && \
+      ((defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 200112L) || \
+       (defined(_XOPEN_SOURCE) && _XOPEN_SOURCE >= 600) || \
+       defined(__APPLE__))
 #    define LUA_USE_POSIX 1
-#  elif (defined(_MSC_VER))
-#    define LUA_USE_WINDOWS 0
 #  endif
 
 typedef struct COMPAT53_luaL_Stream {