diff --git a/x86/bios.c b/x86/bios.c
index 5ac9e24..0f8dd24 100644
--- a/x86/bios.c
+++ b/x86/bios.c
@@ -45,7 +45,7 @@
 		.offset		= handler->address - MB_BIOS_BEGIN,
 	};
 
-	DIE_IF((handler->address - MB_BIOS_BEGIN) > 0xffffUL);
+	DIE_IF((handler->address - MB_BIOS_BEGIN + 1) > MB_BIOS_SIZE);
 
 	interrupt_table__set(&kvm->arch.interrupt_table, &intr_desc, handler->irq);
 }
@@ -75,7 +75,7 @@
 	};
 	mem_map[i++]	= (struct e820entry) {
 		.addr		= MB_BIOS_BEGIN,
-		.size		= MB_BIOS_END - MB_BIOS_BEGIN,
+		.size		= MB_BIOS_SIZE,
 		.type		= E820_RESERVED,
 	};
 	if (kvm->ram_size < KVM_32BIT_GAP_START) {
@@ -132,16 +132,16 @@
 	 * we definitely don't want any trash here
 	 */
 	p = guest_flat_to_host(kvm, BDA_START);
-	memset(p, 0, BDA_END - BDA_START);
+	memset(p, 0, BDA_SIZE);
 
 	p = guest_flat_to_host(kvm, EBDA_START);
-	memset(p, 0, EBDA_END - EBDA_START);
+	memset(p, 0, EBDA_SIZE);
 
 	p = guest_flat_to_host(kvm, MB_BIOS_BEGIN);
-	memset(p, 0, MB_BIOS_END - MB_BIOS_BEGIN);
+	memset(p, 0, MB_BIOS_SIZE);
 
 	p = guest_flat_to_host(kvm, VGA_ROM_BEGIN);
-	memset(p, 0, VGA_ROM_END - VGA_ROM_BEGIN);
+	memset(p, 0, VGA_ROM_SIZE);
 
 	/* just copy the bios rom into the place */
 	p = guest_flat_to_host(kvm, MB_BIOS_BEGIN);
diff --git a/x86/include/kvm/bios.h b/x86/include/kvm/bios.h
index edeab17..6f4338d 100644
--- a/x86/include/kvm/bios.h
+++ b/x86/include/kvm/bios.h
@@ -21,9 +21,11 @@
 
 #define BDA_START			0x00000400
 #define BDA_END				0x000004ff
+#define BDA_SIZE			(BDA_END - BDA_START + 1)
 
 #define EBDA_START			0x0009fc00
 #define EBDA_END			0x0009ffff
+#define EBDA_SIZE			(EBDA_END - EBDA_START + 1)
 
 #define E820_MAP_START			EBDA_START
 
@@ -43,6 +45,7 @@
 #define VGA_ROM_MODES			(VGA_ROM_OEM_STRING + VGA_ROM_OEM_STRING_SIZE)
 #define VGA_ROM_MODES_SIZE		32
 #define VGA_ROM_END			0x000c7fff
+#define VGA_ROM_SIZE			(VGA_ROM_END - VGA_ROM_BEGIN + 1)
 
 /* we handle one page only */
 #define VGA_RAM_SEG			(VGA_RAM_BEGIN >> 4)