diff --git a/hw/acpi/core.c b/hw/acpi/core.c
index b8d39012cd..f467779b3a 100644
--- a/hw/acpi/core.c
+++ b/hw/acpi/core.c
@@ -502,13 +502,21 @@ static inline int64_t acpi_pm_tmr_get_clock(void)
 void acpi_pm_tmr_calc_overflow_time(ACPIREGS *ar)
 {
     int64_t d = acpi_pm_tmr_get_clock();
+#ifdef XBOX
+    ar->tmr.overflow_time = (d + 0x80000000LL) & ~0x7fffffffLL;
+#else
     ar->tmr.overflow_time = (d + 0x800000LL) & ~0x7fffffLL;
+#endif
 }
 
 static uint32_t acpi_pm_tmr_get(ACPIREGS *ar)
 {
     uint32_t d = acpi_pm_tmr_get_clock();
+#ifdef XBOX
+    return d;
+#else
     return d & 0xffffff;
+#endif
 }
 
 static void acpi_pm_tmr_timer(void *opaque)
diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 3cf2a1679c..30c6a061e6 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -130,6 +130,9 @@ static void init_common_fadt_data(Object *o, AcpiFadtData *data)
             (1 << ACPI_FADT_F_SLP_BUTTON) |
             (1 << ACPI_FADT_F_RTC_S4) |
             (1 << ACPI_FADT_F_USE_PLATFORM_CLOCK) |
+#ifdef XBOX
+            (1 << ACPI_FADT_F_TMR_VAL_EXT) |
+#endif
             /* APIC destination mode ("Flat Logical") has an upper limit of 8
              * CPUs for more than 8 CPUs, "Clustered Logical" mode has to be
              * used
diff --git a/include/hw/acpi/acpi.h b/include/hw/acpi/acpi.h
index c20ace0d0b..58c5765d98 100644
--- a/include/hw/acpi/acpi.h
+++ b/include/hw/acpi/acpi.h
@@ -50,7 +50,11 @@
 #define ACPI_PM_PROP_GPE0_BLK_LEN "gpe0_blk_len"
 
 /* PM Timer ticks per second (HZ) */
+#ifdef XBOX
+#define PM_TIMER_FREQUENCY  3375000
+#else
 #define PM_TIMER_FREQUENCY  3579545
+#endif
 
 
 /* ACPI fixed hardware registers */