diff --git a/lib/libc/net/sourcefilter.c b/lib/libc/net/sourcefilter.c
index 2fe9913dbe49..cb64701e6f9e 100644
--- a/lib/libc/net/sourcefilter.c
+++ b/lib/libc/net/sourcefilter.c
@@ -337,8 +337,8 @@ getsourcefilter(int s, uint32_t interface, struct sockaddr *group,
 {
 	struct __msfilterreq	 msfr;
 	sockunion_t		*psu;
+	socklen_t		 optlen;
 	int			 err, level, nsrcs, optname;
-	unsigned int		 optlen;
 
 	if (interface == 0 || group == NULL || numsrc == NULL ||
 	    fmode == NULL) {