diff --git a/OvmfPkg/Include/IndustryStandard/QemuFwCfg.h b/OvmfPkg/Include/IndustryStandard/QemuFwCfg.h
index c7e9b5c382..776bfe88ae 100644
--- a/OvmfPkg/Include/IndustryStandard/QemuFwCfg.h
+++ b/OvmfPkg/Include/IndustryStandard/QemuFwCfg.h
@@ -42,6 +42,12 @@
 #define FW_CFG_DMA_CTL_SELECT BIT3
 #define FW_CFG_DMA_CTL_WRITE  BIT4
 
+//
+// The fw_cfg registers can be found at these IO Ports, on the IO-mapped
+// platforms (Ia32 and X64).
+//
+#define FW_CFG_IO_SELECTOR    0x510
+
 //
 // Numerically defined keys.
 //
diff --git a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c
index 7744873217..1387ea85f3 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c
@@ -42,7 +42,7 @@ QemuFwCfgSelectItem (
   )
 {
   DEBUG ((EFI_D_INFO, "Select Item: 0x%x\n", (UINT16)(UINTN) QemuFwCfgItem));
-  IoWrite16 (0x510, (UINT16)(UINTN) QemuFwCfgItem);
+  IoWrite16 (FW_CFG_IO_SELECTOR, (UINT16)(UINTN) QemuFwCfgItem);
 }
 
 
diff --git a/OvmfPkg/SmmControl2Dxe/SmiFeatures.c b/OvmfPkg/SmmControl2Dxe/SmiFeatures.c
index e070969065..352ffa0173 100644
--- a/OvmfPkg/SmmControl2Dxe/SmiFeatures.c
+++ b/OvmfPkg/SmmControl2Dxe/SmiFeatures.c
@@ -281,7 +281,7 @@ SaveSmiFeatures (
                           S3SaveState,                     // This
                           EFI_BOOT_SCRIPT_IO_WRITE_OPCODE, // OpCode
                           EfiBootScriptWidthUint16,        // Width
-                          (UINT64)0x510,                   // Address
+                          (UINT64)FW_CFG_IO_SELECTOR,      // Address
                           (UINTN)1,                        // Count
                           &FeaturesOkItemAsUint16          // Buffer
                           );