diff --git a/src/soc/intel/common/block/acpi/acpi.c b/src/soc/intel/common/block/acpi/acpi.c
index 3db96a030d..bf4003d575 100644
--- a/src/soc/intel/common/block/acpi/acpi.c
+++ b/src/soc/intel/common/block/acpi/acpi.c
@@ -36,7 +36,7 @@ unsigned long acpi_fill_mcfg(unsigned long current)
 	/* PCI Segment Group 0, Start Bus Number 0, End Bus Number is 255 */
 	current += acpi_create_mcfg_mmconfig((void *)current,
 					     CONFIG_MMCONF_BASE_ADDRESS, 0, 0,
-					     255);
+					     (CONFIG_SA_PCIEX_LENGTH >> 20) - 1);
 	return current;
 }
 
diff --git a/src/soc/intel/skylake/acpi.c b/src/soc/intel/skylake/acpi.c
index 6e1a88657d..202d686d72 100644
--- a/src/soc/intel/skylake/acpi.c
+++ b/src/soc/intel/skylake/acpi.c
@@ -210,7 +210,8 @@ static void acpi_create_gnvs(global_nvs_t *gnvs)
 unsigned long acpi_fill_mcfg(unsigned long current)
 {
 	current += acpi_create_mcfg_mmconfig((acpi_mcfg_mmconfig_t *)current,
-					     MCFG_BASE_ADDRESS, 0, 0, 255);
+					     MCFG_BASE_ADDRESS, 0, 0,
+					     (CONFIG_SA_PCIEX_LENGTH >> 20) - 1);
 	return current;
 }