diff --git a/src/core/pbuf.c b/src/core/pbuf.c
index 0f6a1c8d..1a91d750 100644
--- a/src/core/pbuf.c
+++ b/src/core/pbuf.c
@@ -498,7 +498,7 @@ pbuf_realloc(struct pbuf *p, u16_t new_len)
  * @return non-zero on failure, zero on success.
  *
  */
-u8_t
+static u8_t
 pbuf_header_impl(struct pbuf *p, s16_t header_size_increment, u8_t force)
 {
   u16_t type;