diff --git a/usr.bin/killall/killall.c b/usr.bin/killall/killall.c
index e06d91e2ceac..c7d34f2d679a 100644
--- a/usr.bin/killall/killall.c
+++ b/usr.bin/killall/killall.c
@@ -366,8 +366,8 @@ main(int ac, char **av)
 		killed++;
 		if (!dflag && !sflag) {
 			if (kill(thispid, sig) < 0 /* && errno != ESRCH */ ) {
-				warn("kill -%s %d", upper(sys_signame[sig]),
-				    thispid);
+				warn("warning: kill -%s %d",
+				    upper(sys_signame[sig]), thispid);
 				errors = 1;
 			}
 		}