diff --git a/hw/mips_jazz.c b/hw/mips_jazz.c
index cdf21962047e65ef64f45c199a7506f940dcc387..0dcc332c404be702a532f44500e2ea898914e219 100644
--- a/hw/mips_jazz.c
+++ b/hw/mips_jazz.c
@@ -229,7 +229,7 @@ void mips_jazz_init (ram_addr_t ram_size, int vga_ram_size,
     cpu_register_physical_memory(0x80004000, 0x00001000, s_rtc);
 
     /* Keyboard (i8042) */
-    i8042_mm_init(rc4030[6], rc4030[7], 0x80005000, 0);
+    i8042_mm_init(rc4030[6], rc4030[7], 0x80005000, 0x1000, 0x1);
 
     /* Serial ports */
     if (serial_hds[0])
diff --git a/hw/pc.h b/hw/pc.h
index f156b9ec87bb7efc114b6283f34565303bb0803c..39b220ff85248b0f6ec2ae2c79fe57b27f316525 100644
--- a/hw/pc.h
+++ b/hw/pc.h
@@ -71,7 +71,8 @@ void *vmmouse_init(void *m);
 
 void i8042_init(qemu_irq kbd_irq, qemu_irq mouse_irq, uint32_t io_base);
 void i8042_mm_init(qemu_irq kbd_irq, qemu_irq mouse_irq,
-                   target_phys_addr_t base, int it_shift);
+                   target_phys_addr_t base, ram_addr_t size,
+                   target_phys_addr_t mask);
 
 /* mc146818rtc.c */
 
diff --git a/hw/pckbd.c b/hw/pckbd.c
index cceea4a5d1ecb771645c25179affca25b510c7c8..3a004f7a8ef3475ab708ceb2a6c610e562981540 100644
--- a/hw/pckbd.c
+++ b/hw/pckbd.c
@@ -125,7 +125,7 @@ typedef struct KBDState {
 
     qemu_irq irq_kbd;
     qemu_irq irq_mouse;
-    int it_shift;
+    target_phys_addr_t mask;
 } KBDState;
 
 static KBDState kbd_state;
@@ -391,28 +391,20 @@ static uint32_t kbd_mm_readb (void *opaque, target_phys_addr_t addr)
 {
     KBDState *s = opaque;
 
-    switch (addr >> s->it_shift) {
-    case 0:
-        return kbd_read_data(s, 0) & 0xff;
-    case 1:
+    if (addr & s->mask)
         return kbd_read_status(s, 0) & 0xff;
-    default:
-        return 0xff;
-    }
+    else
+        return kbd_read_data(s, 0) & 0xff;
 }
 
 static void kbd_mm_writeb (void *opaque, target_phys_addr_t addr, uint32_t value)
 {
     KBDState *s = opaque;
 
-    switch (addr >> s->it_shift) {
-    case 0:
-        kbd_write_data(s, 0, value & 0xff);
-        break;
-    case 1:
+    if (addr & s->mask)
         kbd_write_command(s, 0, value & 0xff);
-        break;
-    }
+    else
+        kbd_write_data(s, 0, value & 0xff);
 }
 
 static CPUReadMemoryFunc *kbd_mm_read[] = {
@@ -428,19 +420,20 @@ static CPUWriteMemoryFunc *kbd_mm_write[] = {
 };
 
 void i8042_mm_init(qemu_irq kbd_irq, qemu_irq mouse_irq,
-                   target_phys_addr_t base, int it_shift)
+                   target_phys_addr_t base, ram_addr_t size,
+                   target_phys_addr_t mask)
 {
     KBDState *s = &kbd_state;
     int s_io_memory;
 
     s->irq_kbd = kbd_irq;
     s->irq_mouse = mouse_irq;
-    s->it_shift = it_shift;
+    s->mask = mask;
 
     kbd_reset(s);
     register_savevm("pckbd", 0, 3, kbd_save, kbd_load, s);
     s_io_memory = cpu_register_io_memory(0, kbd_mm_read, kbd_mm_write, s);
-    cpu_register_physical_memory(base, 2 << it_shift, s_io_memory);
+    cpu_register_physical_memory(base, size, s_io_memory);
 
     s->kbd = ps2_kbd_init(kbd_update_kbd_irq, s);
     s->mouse = ps2_mouse_init(kbd_update_aux_irq, s);