diff --git a/src/core/ipv4/inet_chksum.c b/src/core/ipv4/inet_chksum.c
index 1ad15a9b..9bba4f4c 100644
--- a/src/core/ipv4/inet_chksum.c
+++ b/src/core/ipv4/inet_chksum.c
@@ -36,13 +36,13 @@
  *
  */
 
-#include <string.h>
-
 #include "lwip/opt.h"
 
 #include "lwip/inet_chksum.h"
 #include "lwip/inet.h"
 
+#include <string.h>
+
 /* These are some reference implementations of the checksum algorithm, with the
  * aim of being simple, correct and fully portable. Checksumming is the
  * first thing you would want to optimize for your platform. If you create