diff --git a/lib/iomap.c b/lib/iomap.c
index dd6ca48..37a3ea4 100644
--- a/lib/iomap.c
+++ b/lib/iomap.c
@@ -257,7 +257,7 @@
 void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long maxlen)
 {
 	resource_size_t start = pci_resource_start(dev, bar);
-	unsigned long len = pci_resource_len(dev, bar);
+	resource_size_t len = pci_resource_len(dev, bar);
 	unsigned long flags = pci_resource_flags(dev, bar);
 
 	if (!len || !start)