diff --git a/MdeModulePkg/Bus/Ata/AhciPei/AhciPeiPassThru.c b/MdeModulePkg/Bus/Ata/AhciPei/AhciPeiPassThru.c
index 7bd04661d0..a77ecfc6a2 100644
--- a/MdeModulePkg/Bus/Ata/AhciPei/AhciPeiPassThru.c
+++ b/MdeModulePkg/Bus/Ata/AhciPei/AhciPeiPassThru.c
@@ -384,6 +384,10 @@ Exit:
   If PortMultiplierPort is the port multiplier port number of the last ATA device
   on the port of the ATA controller, then EFI_NOT_FOUND is returned.
 
+  When port multiplier is not connected to the Port, GetNextDevice() may either return
+  EFI_SUCCESS and set PortMultiplierPort to 0xFFFF or return EFI_NOT_FOUND (in which case the
+  PortMultiplierPort value is undefined).
+
   @param[in]     This                  The PPI instance pointer.
   @param[in]     Port                  The port number present on the ATA controller.
   @param[in,out] PortMultiplierPort    On input, a pointer to the port multiplier
diff --git a/MdeModulePkg/Bus/Ata/AtaAtapiPassThru/AtaAtapiPassThru.c b/MdeModulePkg/Bus/Ata/AtaAtapiPassThru/AtaAtapiPassThru.c
index f39c909d06..986b3e2344 100644
--- a/MdeModulePkg/Bus/Ata/AtaAtapiPassThru/AtaAtapiPassThru.c
+++ b/MdeModulePkg/Bus/Ata/AtaAtapiPassThru/AtaAtapiPassThru.c
@@ -1541,6 +1541,10 @@ Exit:
   If PortMultiplierPort is the port multiplier port number of the last ATA device on the port of
   the ATA controller, then EFI_NOT_FOUND is returned.
 
+  When port multiplier is not connected to the Port, GetNextDevice() may either return
+  EFI_SUCCESS and set PortMultiplierPort to 0xFFFF or return EFI_NOT_FOUND (in which case the
+  PortMultiplierPort value is undefined).
+
   @param[in]      This               A pointer to the EFI_ATA_PASS_THRU_PROTOCOL instance.
   @param[in]      Port               The port number present on the ATA controller.
   @param[in, out] PortMultiplierPort On input, a pointer to the port multiplier port number of an
diff --git a/MdeModulePkg/Include/Ppi/AtaPassThru.h b/MdeModulePkg/Include/Ppi/AtaPassThru.h
index 73fb688c8a..d0e05ae4ff 100644
--- a/MdeModulePkg/Include/Ppi/AtaPassThru.h
+++ b/MdeModulePkg/Include/Ppi/AtaPassThru.h
@@ -141,6 +141,10 @@ EFI_STATUS
   If PortMultiplierPort is the port multiplier port number of the last ATA device
   on the port of the ATA controller, then EFI_NOT_FOUND is returned.
 
+  When port multiplier is not connected to the Port, GetNextDevice() may either return
+  EFI_SUCCESS and set PortMultiplierPort to 0xFFFF or return EFI_NOT_FOUND (in which case the
+  PortMultiplierPort value is undefined).
+
   @param[in]     This                  The PPI instance pointer.
   @param[in]     Port                  The port number present on the ATA controller.
   @param[in,out] PortMultiplierPort    On input, a pointer to the port multiplier