diff --git a/c-programming/reverse-ramdisk.c b/c-programming/reverse-ramdisk.c
index aca186c..0fe67b2 100644
--- a/c-programming/reverse-ramdisk.c
+++ b/c-programming/reverse-ramdisk.c
@@ -20,7 +20,7 @@ To-Do: Add thread-safe versions of functions (use postfix `_r`)
 #include <stdlib.h>
 #include <string.h>
 
-#if _POSIX_VERSION >= 200809L && defined(_POSIX_SYNCHRONIZED_IO)
+#if _POSIX_VERSION >= 200112L
 # include <fcntl.h>
 # include <unistd.h>
 # define IS_POSIX 1