diff --git a/doc/changelog.txt b/doc/changelog.txt
index e3f421f..770ac06 100644
--- a/doc/changelog.txt
+++ b/doc/changelog.txt
@@ -1,6 +1,8 @@
 
 HEAD
 ====
+Enhancements:
+- support for Linux up to 4.15
 
 
 v2.14 (2017-11-22)
diff --git a/extensions/pknock/xt_pknock.c b/extensions/pknock/xt_pknock.c
index 31d4bc8..3f47d9b 100644
--- a/extensions/pknock/xt_pknock.c
+++ b/extensions/pknock/xt_pknock.c
@@ -357,14 +357,11 @@ has_logged_during_this_minute(const struct peer *peer)
  *
  * @r: rule
  */
-static void
-peer_gc(
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 15, 0)
-	struct timer_list *tl
+static void peer_gc(struct timer_list *tl)
 #else
-	unsigned long r
+static void peer_gc(unsigned long r)
 #endif
-)
 {
 	unsigned int i;
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 15, 0)