diff --git a/OvmfPkg/OvmfPkg.fdf.inc b/OvmfPkg/OvmfPkg.fdf.inc
index 9cc0578d64..f12d61c2b6 100644
--- a/OvmfPkg/OvmfPkg.fdf.inc
+++ b/OvmfPkg/OvmfPkg.fdf.inc
@@ -15,18 +15,11 @@
 #
 ##
 
-#
-# Default flash size is 2MB.
-#
-# Defining FD_SIZE_1MB on the build command line can override this.
-#
-
 DEFINE BLOCK_SIZE        = 0x1000
 DEFINE VARS_SIZE         = 0x20000
 DEFINE VARS_BLOCKS       = 0x20
 
-!ifdef $(FD_SIZE_1MB)
-
+!if $(FD_SIZE_IN_KB) == 1024
 DEFINE FW_BASE_ADDRESS   = 0xFFF00000
 DEFINE FW_SIZE           = 0x00100000
 DEFINE FW_BLOCKS         = 0x100
@@ -36,9 +29,9 @@ DEFINE CODE_BLOCKS       = 0xE0
 DEFINE FVMAIN_SIZE       = 0x000CC000
 DEFINE SECFV_OFFSET      = 0x000EC000
 DEFINE SECFV_SIZE        = 0x14000
+!endif
 
-!else
-
+!if $(FD_SIZE_IN_KB) == 2048
 DEFINE FW_BASE_ADDRESS   = 0xFFE00000
 DEFINE FW_SIZE           = 0x00200000
 DEFINE FW_BLOCKS         = 0x200
@@ -48,7 +41,6 @@ DEFINE CODE_BLOCKS       = 0x1E0
 DEFINE FVMAIN_SIZE       = 0x001AC000
 DEFINE SECFV_OFFSET      = 0x001CC000
 DEFINE SECFV_SIZE        = 0x34000
-
 !endif
 
 SET gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFdBaseAddress     = $(FW_BASE_ADDRESS)
diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
index 0796b0db81..5a21840a55 100644
--- a/OvmfPkg/OvmfPkgIa32.dsc
+++ b/OvmfPkg/OvmfPkgIa32.dsc
@@ -40,6 +40,21 @@
   DEFINE SMM_REQUIRE             = FALSE
   DEFINE TLS_ENABLE              = FALSE
 
+  #
+  # Flash size selection. Setting FD_SIZE_IN_KB on the command line directly to
+  # one of the supported values, in place of any of the convenience macros, is
+  # permitted.
+  #
+!ifdef $(FD_SIZE_1MB)
+  DEFINE FD_SIZE_IN_KB           = 1024
+!else
+!ifdef $(FD_SIZE_2MB)
+  DEFINE FD_SIZE_IN_KB           = 2048
+!else
+  DEFINE FD_SIZE_IN_KB           = 2048
+!endif
+!endif
+
 [BuildOptions]
   GCC:*_UNIXGCC_*_CC_FLAGS             = -DMDEPKG_NDEBUG
   GCC:RELEASE_*_*_CC_FLAGS             = -DMDEPKG_NDEBUG
diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc
index 71ac62f023..11866b7207 100644
--- a/OvmfPkg/OvmfPkgIa32X64.dsc
+++ b/OvmfPkg/OvmfPkgIa32X64.dsc
@@ -40,6 +40,21 @@
   DEFINE SMM_REQUIRE             = FALSE
   DEFINE TLS_ENABLE              = FALSE
 
+  #
+  # Flash size selection. Setting FD_SIZE_IN_KB on the command line directly to
+  # one of the supported values, in place of any of the convenience macros, is
+  # permitted.
+  #
+!ifdef $(FD_SIZE_1MB)
+  DEFINE FD_SIZE_IN_KB           = 1024
+!else
+!ifdef $(FD_SIZE_2MB)
+  DEFINE FD_SIZE_IN_KB           = 2048
+!else
+  DEFINE FD_SIZE_IN_KB           = 2048
+!endif
+!endif
+
 [BuildOptions]
   GCC:*_UNIXGCC_*_CC_FLAGS             = -DMDEPKG_NDEBUG
   GCC:RELEASE_*_*_CC_FLAGS             = -DMDEPKG_NDEBUG
diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
index 2ceb31d7ff..2fab544600 100644
--- a/OvmfPkg/OvmfPkgX64.dsc
+++ b/OvmfPkg/OvmfPkgX64.dsc
@@ -40,6 +40,21 @@
   DEFINE SMM_REQUIRE             = FALSE
   DEFINE TLS_ENABLE              = FALSE
 
+  #
+  # Flash size selection. Setting FD_SIZE_IN_KB on the command line directly to
+  # one of the supported values, in place of any of the convenience macros, is
+  # permitted.
+  #
+!ifdef $(FD_SIZE_1MB)
+  DEFINE FD_SIZE_IN_KB           = 1024
+!else
+!ifdef $(FD_SIZE_2MB)
+  DEFINE FD_SIZE_IN_KB           = 2048
+!else
+  DEFINE FD_SIZE_IN_KB           = 2048
+!endif
+!endif
+
 [BuildOptions]
   GCC:*_UNIXGCC_*_CC_FLAGS             = -DMDEPKG_NDEBUG
   GCC:RELEASE_*_*_CC_FLAGS             = -DMDEPKG_NDEBUG