diff --git a/common/hw-gfx-gma.adb b/common/hw-gfx-gma.adb
index 269feec..8352e1c 100644
--- a/common/hw-gfx-gma.adb
+++ b/common/hw-gfx-gma.adb
@@ -38,7 +38,8 @@
 package body HW.GFX.GMA
    with Refined_State =>
      (State =>
-        (Dev.Address_State,
+        (PCI_Usable,
+         Dev.Address_State,
          Registers.Address_State,
          PCode.Mailbox_Ready,
          PLLs.State, Panel.Panel_State,
@@ -384,7 +385,8 @@
         (Input => (Time.State),
          In_Out => (Dev.PCI_State, Registers.Register_State, Port_IO.State),
          Output =>
-           (Config.Variable,
+           (PCI_Usable,
+            Config.Variable,
             Dev.Address_State,
             Registers.Address_State,
             PCode.Mailbox_Ready,
@@ -446,6 +448,7 @@
 
       pragma Debug (Debug.Set_Register_Write_Delay (Write_Delay));
 
+      PCI_Usable := False;
       Linear_FB_Base := 0;
       PCode.Mailbox_Ready := False;
       Wait_For_HPD := HPD_Type'(others => False);
@@ -470,6 +473,7 @@
             Dev.Map (PCI_GTT_Base, PCI.Res0, Offset => MMIO_GTT_Offset);
             if PCI_MMIO_Base /= 0 and PCI_GTT_Base /= 0 then
                Registers.Set_Register_Base (PCI_MMIO_Base, PCI_GTT_Base);
+               PCI_Usable := True;
             else
                pragma Debug (Debug.Put_Line
                  ("ERROR: Couldn't map resoure0."));
@@ -934,4 +938,11 @@
       end loop;
    end Dump_Configs;
 
+   ----------------------------------------------------------------------------
+
+   procedure PCI_Read16 (Value : out Word16; Offset : HW.PCI.Index) is
+   begin
+      Dev.Read16 (Value, Offset);
+   end PCI_Read16;
+
 end HW.GFX.GMA;
diff --git a/common/hw-gfx-gma.ads b/common/hw-gfx-gma.ads
index 353ec4b..3a4580e 100644
--- a/common/hw-gfx-gma.ads
+++ b/common/hw-gfx-gma.ads
@@ -15,6 +15,7 @@
 
 with HW.Config;
 with HW.Time;
+with HW.PCI;
 with HW.Port_IO;
 with HW.GFX.Framebuffer_Filler;
 
@@ -230,6 +231,14 @@
 
 private
 
+   PCI_Usable : Boolean with Part_Of => State;
+   use type HW.PCI.Index;
+   procedure PCI_Read16 (Value : out Word16; Offset : HW.PCI.Index)
+   with
+      Pre => PCI_Usable and Offset mod 2 = 0;
+
+   ----------------------------------------------------------------------------
+
    -- For the default framebuffer setup (see below) with 90 degree rotations,
    -- we expect the offset which is used for the final scanout to be above
    -- `GTT_Rotation_Offset`. So we can use `Offset - GTT_Rotation_Offset` for