diff --git a/bmon.c b/bmon.c
index ddd9d0f..17d2797 100644
--- a/bmon.c
+++ b/bmon.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 200809L
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/types.h>
diff --git a/makefile b/makefile
index 559ff91..dc236c2 100644
--- a/makefile
+++ b/makefile
@@ -1,5 +1,5 @@
 CC = gcc
-CFLAGS = -Wall -pedantic -O2
+CFLAGS = -Wall -pedantic --std=c99 -O2
 
 bmon: bmon.o