diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index b6acc3a..d679010 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -42,7 +42,7 @@
 
 	e820.nr_map = 0;
 
-	e820_add_region(0, PFN_PHYS(max_pfn), E820_RAM);
+	e820_add_region(0, PFN_PHYS((u64)max_pfn), E820_RAM);
 
 	/*
 	 * Even though this is normal, usable memory under Xen, reserve