diff --git a/TODO b/TODO
index 2c3d23c..16d66e3 100644
--- a/TODO
+++ b/TODO
@@ -1,5 +1,5 @@
 [x] use system lua lib
-[ ] make it std=c11 not gnu11
+[x] make it std=c11 not gnu11
 [ ] make it compile on openbsd
 [ ] update license, readme and documentation
 [ ] add manpage
diff --git a/makefile b/makefile
index 88662c2..45c98c6 100644
--- a/makefile
+++ b/makefile
@@ -4,7 +4,7 @@ PREFIX = /usr/local
 MANPREFIX = ${PREFIX}/share/man
 CC ?= gcc
 SRCDIR = ./src
-CFLAGS = -Wall -Werror -pedantic -O3 -std=gnu11 -fno-strict-aliasing \
+CFLAGS = -Wall -Werror -pedantic -O3 -std=c11 -fno-strict-aliasing \
 	-I${SRCDIR} -DLUA_USE_POSIX
 # remove this
 LDFLAGS = -lSDL2 -lm -llua5.2
diff --git a/src/api/system.c b/src/api/system.c
index da474eb..872800a 100644
--- a/src/api/system.c
+++ b/src/api/system.c
@@ -1,10 +1,16 @@
-#include <SDL2/SDL.h>
+#define _XOPEN_SOURCE 700
+
+#include <sys/stat.h>
+
 #include <stdbool.h>
 #include <ctype.h>
 #include <dirent.h>
 #include <unistd.h>
 #include <errno.h>
-#include <sys/stat.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <SDL2/SDL.h>
+
 #include "api.h"
 #include "rencache.h"
 
diff --git a/src/main.c b/src/main.c
index f47e93b..d599118 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,3 +1,5 @@
+#define _POSIX_C_SOURCE 200809l
+
 #include <stdio.h>
 #include <unistd.h>
 #include <SDL2/SDL.h>
@@ -5,10 +7,8 @@
 #include "api/api.h"
 #include "renderer.h"
 
-
 SDL_Window *window;
 
-
 static double get_scale(void)
 {
 	float dpi;
@@ -16,7 +16,6 @@ static double get_scale(void)
 	return 1.0;
 }
 
-
 static void get_exe_filename(char *buf, int sz)
 {
 	char path[512];
@@ -25,7 +24,6 @@ static void get_exe_filename(char *buf, int sz)
 	buf[len] = '\0';
 }
 
-
 static void init_window_icon(void)
 {
 	// FIXME: include inside function!?