diff --git a/networking/isrv.c b/networking/isrv.c
index 1c6491e..3673db7 100644
--- a/networking/isrv.c
+++ b/networking/isrv.c
@@ -194,7 +194,6 @@
 		remove_peer(state, n); /* unsuccesful peer start */
 }
 
-void BUG_sizeof_fd_set_is_strange(void);
 static void handle_fd_set(isrv_state_t *state, fd_set *fds, int (*h)(int, void **))
 {
 	enum { LONG_CNT = sizeof(fd_set) / sizeof(long) };
@@ -203,8 +202,7 @@
 	/* need to know value at _the beginning_ of this routine */
 	int fd_cnt = FD_COUNT;
 
-	if (LONG_CNT * sizeof(long) != sizeof(fd_set))
-		BUG_sizeof_fd_set_is_strange();
+	BUILD_BUG_ON(LONG_CNT * sizeof(long) != sizeof(fd_set));
 
 	fds_pos = 0;
 	while (1) {