diff --git a/src/core/inet_chksum.c b/src/core/inet_chksum.c
index 448cc5b8..01a8fa96 100644
--- a/src/core/inet_chksum.c
+++ b/src/core/inet_chksum.c
@@ -79,7 +79,7 @@ u16_t lwip_standard_chksum(void *dataptr, int len);
  * @note host endianess is irrelevant (p3 RFC1071)
  */
 u16_t
-lwip_standard_chksum(void *dataptr, u16_t len)
+lwip_standard_chksum(void *dataptr, int len)
 {
   u32_t acc;
   u16_t src;