diff --git a/docs/system/arm/nuvoton.rst b/docs/system/arm/nuvoton.rst
index 0424cae4b0..e611099545 100644
--- a/docs/system/arm/nuvoton.rst
+++ b/docs/system/arm/nuvoton.rst
@@ -50,6 +50,8 @@ Supported devices
  * Ethernet controller (EMC)
  * Tachometer
  * Peripheral SPI controller (PSPI)
+ * BIOS POST code FIFO
+ * PCI Mailbox
 
 Missing devices
 ---------------
diff --git a/hw/arm/npcm7xx.c b/hw/arm/npcm7xx.c
index 15ff21d047..c9e87162cb 100644
--- a/hw/arm/npcm7xx.c
+++ b/hw/arm/npcm7xx.c
@@ -53,6 +53,9 @@
 /* ADC Module */
 #define NPCM7XX_ADC_BA          (0xf000c000)
 
+/* PCI Mailbox Module */
+#define NPCM7XX_PCI_MBOX_BA     (0xf0848000)
+
 /* Internal AHB SRAM */
 #define NPCM7XX_RAM3_BA         (0xc0008000)
 #define NPCM7XX_RAM3_SZ         (4 * KiB)
@@ -83,6 +86,9 @@ enum NPCM7xxInterrupt {
     NPCM7XX_UART1_IRQ,
     NPCM7XX_UART2_IRQ,
     NPCM7XX_UART3_IRQ,
+    NPCM7XX_PCI_MBOX_IRQ        = 8,
+    NPCM7XX_KCS_HIB_IRQ         = 9,
+    NPCM7XX_GMAC1_IRQ           = 14,
     NPCM7XX_EMC1RX_IRQ          = 15,
     NPCM7XX_EMC1TX_IRQ,
     NPCM7XX_MMC_IRQ             = 26,
@@ -456,6 +462,8 @@ static void npcm7xx_init(Object *obj)
         object_initialize_child(obj, "pspi[*]", &s->pspi[i], TYPE_NPCM_PSPI);
     }
 
+    object_initialize_child(obj, "pci-mbox", &s->pci_mbox,
+                            TYPE_NPCM7XX_PCI_MBOX);
     object_initialize_child(obj, "mmc", &s->mmc, TYPE_NPCM7XX_SDHCI);
 }
 
@@ -706,6 +714,14 @@ static void npcm7xx_realize(DeviceState *dev, Error **errp)
         }
     }
 
+    /* PCI Mailbox. Cannot fail */
+    sysbus_realize(SYS_BUS_DEVICE(&s->pci_mbox), &error_abort);
+    sysbus_mmio_map(SYS_BUS_DEVICE(&s->pci_mbox), 0, NPCM7XX_PCI_MBOX_BA);
+    sysbus_mmio_map(SYS_BUS_DEVICE(&s->pci_mbox), 1,
+        NPCM7XX_PCI_MBOX_BA + NPCM7XX_PCI_MBOX_RAM_SIZE);
+    sysbus_connect_irq(SYS_BUS_DEVICE(&s->pci_mbox), 0,
+                       npcm7xx_irq(s, NPCM7XX_PCI_MBOX_IRQ));
+
     /* RAM2 (SRAM) */
     memory_region_init_ram(&s->sram, OBJECT(dev), "ram2",
                            NPCM7XX_RAM2_SZ, &error_abort);
@@ -765,7 +781,6 @@ static void npcm7xx_realize(DeviceState *dev, Error **errp)
     create_unimplemented_device("npcm7xx.usbd[8]",      0xf0838000,   4 * KiB);
     create_unimplemented_device("npcm7xx.usbd[9]",      0xf0839000,   4 * KiB);
     create_unimplemented_device("npcm7xx.sd",           0xf0840000,   8 * KiB);
-    create_unimplemented_device("npcm7xx.pcimbx",       0xf0848000, 512 * KiB);
     create_unimplemented_device("npcm7xx.aes",          0xf0858000,   4 * KiB);
     create_unimplemented_device("npcm7xx.des",          0xf0859000,   4 * KiB);
     create_unimplemented_device("npcm7xx.sha",          0xf085a000,   4 * KiB);
diff --git a/hw/misc/npcm7xx_pci_mbox.c b/hw/misc/npcm7xx_pci_mbox.c
index dc56e2bd5a..0ac8391479 100644
--- a/hw/misc/npcm7xx_pci_mbox.c
+++ b/hw/misc/npcm7xx_pci_mbox.c
@@ -76,22 +76,28 @@ static void npcm7xx_pci_mbox_send_response(NPCM7xxPCIMBoxState *s, uint8_t code)
 
 static void npcm7xx_pci_mbox_handle_read(NPCM7xxPCIMBoxState *s)
 {
+    uint8_t offset_bytes[4];
     MemTxResult r = memory_region_dispatch_read(
         &s->ram, s->offset, &s->data, MO_LE | size_memop(s->size),
         MEMTXATTRS_UNSPECIFIED);
 
-    npcm7xx_pci_mbox_send_response(s, (uint8_t)r);
+    stl_le_p(offset_bytes, r);
+    npcm7xx_pci_mbox_send_response(s, offset_bytes[0]);
 }
 
 static void npcm7xx_pci_mbox_handle_write(NPCM7xxPCIMBoxState *s)
 {
+    uint8_t offset_bytes[4];
     MemTxResult r = memory_region_dispatch_write(
         &s->ram, s->offset, s->data, MO_LE | size_memop(s->size),
         MEMTXATTRS_UNSPECIFIED);
 
-    npcm7xx_pci_mbox_send_response(s, (uint8_t)r);
+    stl_le_p(offset_bytes, r);
+    npcm7xx_pci_mbox_send_response(s, offset_bytes[0]);
 }
 
+// The device is using a Little Endian Protocol.
+// If running into errors, please check what protocol is being expected.
 static void npcm7xx_pci_mbox_receive_char(NPCM7xxPCIMBoxState *s, uint8_t byte)
 {
     switch (s->state) {
diff --git a/include/hw/arm/npcm7xx.h b/include/hw/arm/npcm7xx.h
index 72c7722096..cec3792a2e 100644
--- a/include/hw/arm/npcm7xx.h
+++ b/include/hw/arm/npcm7xx.h
@@ -26,6 +26,7 @@
 #include "hw/misc/npcm7xx_clk.h"
 #include "hw/misc/npcm7xx_gcr.h"
 #include "hw/misc/npcm7xx_mft.h"
+#include "hw/misc/npcm7xx_pci_mbox.h"
 #include "hw/misc/npcm7xx_pwm.h"
 #include "hw/misc/npcm7xx_rng.h"
 #include "hw/net/npcm7xx_emc.h"
@@ -104,6 +105,7 @@ struct NPCM7xxState {
     OHCISysBusState     ohci;
     NPCM7xxFIUState     fiu[2];
     NPCM7xxEMCState     emc[2];
+    NPCM7xxPCIMBoxState pci_mbox;
     NPCM7xxSDHCIState   mmc;
     NPCMPSPIState       pspi[2];
 };
