diff --git a/src/channel.c b/src/channel.c
index ee5b512..33605d4 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -4180,7 +4180,7 @@
  * Return TRUE when there is any channel with a keep_open flag.
  */
     int
-channel_any_keep_open()
+channel_any_keep_open(void)
 {
     channel_T	*channel;