diff --git a/serve_image.c b/serve_image.c
index d3794ec..cbcf3b7 100644
--- a/serve_image.c
+++ b/serve_image.c
@@ -1,5 +1,5 @@
 #define PROGRAM_NAME "serve_image"
-#define _POSIX_C_SOURCE 199309
+#define _POSIX_C_SOURCE 200112L
 
 #include <time.h>
 #include <errno.h>