diff --git a/kernel/resource.c b/kernel/resource.c
index ac5f3a3..78b0872 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -787,7 +787,7 @@
 	static struct resource reserve[MAXRESERVE];
 
 	for (;;) {
-		int io_start, io_num;
+		unsigned int io_start, io_num;
 		int x = reserved;
 
 		if (get_option (&str, &io_start) != 2)