diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index dc2ca8ad3603aba73b8a4ed8c78478c74e31ba4a..e0a39595bde3b342c8364a4306f3b8ea61d88def 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -13,6 +13,7 @@
 #include <asm/vdso.h>
 #include <asm/e820.h>
 #include <asm/setup.h>
+#include <asm/acpi.h>
 #include <asm/xen/hypervisor.h>
 #include <asm/xen/hypercall.h>
 
@@ -41,8 +42,15 @@ char * __init xen_memory_setup(void)
 
 	e820.nr_map = 0;
 
-	e820_add_region(0, LOWMEMSIZE(), E820_RAM);
-	e820_add_region(HIGH_MEMORY, PFN_PHYS(max_pfn)-HIGH_MEMORY, E820_RAM);
+	e820_add_region(0, PFN_PHYS(max_pfn), E820_RAM);
+
+	/*
+	 * Even though this is normal, usable memory under Xen, reserve
+	 * ISA memory anyway because too many things think they can poke
+	 * about in there.
+	 */
+	e820_add_region(ISA_START_ADDRESS, ISA_END_ADDRESS - ISA_START_ADDRESS,
+			E820_RESERVED);
 
 	/*
 	 * Reserve Xen bits: