diff --git a/contrib/ipfilter/tools/ipf.c b/contrib/ipfilter/tools/ipf.c
index 901728b5cc7c..a3c0b2bff04b 100644
--- a/contrib/ipfilter/tools/ipf.c
+++ b/contrib/ipfilter/tools/ipf.c
@@ -410,12 +410,16 @@ static void flushfilter(arg, filter)
 		return;
 	}
 
-	if (strchr(arg, 'i') || strchr(arg, 'I'))
+	else if (strchr(arg, 'i') || strchr(arg, 'I'))
 		fl = FR_INQUE;
-	if (strchr(arg, 'o') || strchr(arg, 'O'))
+	else if (strchr(arg, 'o') || strchr(arg, 'O'))
 		fl = FR_OUTQUE;
-	if (strchr(arg, 'a') || strchr(arg, 'A'))
+	else if (strchr(arg, 'a') || strchr(arg, 'A'))
 		fl = FR_OUTQUE|FR_INQUE;
+	else {
+		fprintf(stderr, "Incorrect flush argument: %s\n", arg);
+		usage();
+	}
 	if (opts & OPT_INACTIVE)
 		fl |= FR_INACTIVE;
 	rem = fl;