diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
index d4b5c69..2dbd96c 100644
--- a/drivers/pci/setup-res.c
+++ b/drivers/pci/setup-res.c
@@ -129,7 +129,7 @@
 	resource_size_t size, min, align;
 	int ret;
 
-	size = res->end - res->start + 1;
+	size = resource_size(res);
 	min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO : PCIBIOS_MIN_MEM;
 
 	align = resource_alignment(res);