diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
index 66e944436a..4301e78219 100644
--- a/OvmfPkg/OvmfPkgIa32.dsc
+++ b/OvmfPkg/OvmfPkgIa32.dsc
@@ -30,6 +30,7 @@
   #
   DEFINE SECURE_BOOT_ENABLE      = FALSE
   DEFINE SMM_REQUIRE             = FALSE
+  DEFINE SOURCE_DEBUG_ENABLE     = FALSE
   DEFINE TPM2_ENABLE             = FALSE
   DEFINE TPM2_CONFIG_ENABLE      = FALSE
 
@@ -157,7 +158,7 @@
   CustomizedDisplayLib|MdeModulePkg/Library/CustomizedDisplayLib/CustomizedDisplayLib.inf
   FrameBufferBltLib|MdeModulePkg/Library/FrameBufferBltLib/FrameBufferBltLib.inf
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   PeCoffExtraActionLib|SourceLevelDebugPkg/Library/PeCoffExtraActionLibDebug/PeCoffExtraActionLibDebug.inf
   DebugCommunicationLib|SourceLevelDebugPkg/Library/DebugCommunicationLibSerialPort/DebugCommunicationLibSerialPort.inf
 !else
@@ -225,7 +226,7 @@
 !endif
   ReportStatusCodeLib|MdeModulePkg/Library/PeiReportStatusCodeLib/PeiReportStatusCodeLib.inf
   ExtractGuidedSectionLib|MdePkg/Library/BaseExtractGuidedSectionLib/BaseExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgentLib.inf
 !endif
   HobLib|MdePkg/Library/PeiHobLib/PeiHobLib.inf
@@ -267,7 +268,7 @@
   PeCoffLib|MdePkg/Library/BasePeCoffLib/BasePeCoffLib.inf
   ResourcePublicationLib|MdePkg/Library/PeiResourcePublicationLib/PeiResourcePublicationLib.inf
   ExtractGuidedSectionLib|MdePkg/Library/PeiExtractGuidedSectionLib/PeiExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgentLib.inf
 !endif
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuExceptionHandlerLib.inf
@@ -292,7 +293,7 @@
   DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
 !endif
   ExtractGuidedSectionLib|MdePkg/Library/DxeExtractGuidedSectionLib/DxeExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgentLib.inf
 !endif
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeCpuExceptionHandlerLib.inf
@@ -351,7 +352,7 @@
 !else
   LockBoxLib|OvmfPkg/Library/LockBoxLib/LockBoxDxeLib.inf
 !endif
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgentLib.inf
 !endif
   PciLib|OvmfPkg/Library/DxePciLibI440FxQ35/DxePciLibI440FxQ35.inf
@@ -389,7 +390,7 @@
   DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
 !endif
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/SmmCpuExceptionHandlerLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/SmmDebugAgentLib.inf
 !endif
   BaseCryptLib|CryptoPkg/Library/BaseCryptLib/SmmCryptLib.inf
@@ -481,7 +482,7 @@
   # DEBUG_ERROR     0x80000000  // Error
   gEfiMdePkgTokenSpaceGuid.PcdDebugPrintErrorLevel|0x8000004F
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask|0x17
 !else
   gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask|0x2F
@@ -495,7 +496,7 @@
   # never lets the RAM below 4 GB exceed 2816 MB.
   gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress|0xB0000000
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   gEfiSourceLevelDebugPkgTokenSpaceGuid.PcdDebugLoadImageMethod|0x2
 !endif
 
diff --git a/OvmfPkg/OvmfPkgIa32.fdf b/OvmfPkg/OvmfPkgIa32.fdf
index 785affeb90..586bbff085 100644
--- a/OvmfPkg/OvmfPkgIa32.fdf
+++ b/OvmfPkg/OvmfPkgIa32.fdf
@@ -260,7 +260,7 @@ INF  MdeModulePkg/Universal/DisplayEngineDxe/DisplayEngineDxe.inf
 INF  MdeModulePkg/Universal/MemoryTest/NullMemoryTestDxe/NullMemoryTestDxe.inf
 
 INF  OvmfPkg/SioBusDxe/SioBusDxe.inf
-!ifndef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == FALSE
 INF  MdeModulePkg/Bus/Pci/PciSioSerialDxe/PciSioSerialDxe.inf
 !endif
 INF  MdeModulePkg/Bus/Isa/Ps2KeyboardDxe/Ps2KeyboardDxe.inf
diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc
index 51c2bfb44f..803fd74ae8 100644
--- a/OvmfPkg/OvmfPkgIa32X64.dsc
+++ b/OvmfPkg/OvmfPkgIa32X64.dsc
@@ -30,6 +30,7 @@
   #
   DEFINE SECURE_BOOT_ENABLE      = FALSE
   DEFINE SMM_REQUIRE             = FALSE
+  DEFINE SOURCE_DEBUG_ENABLE     = FALSE
   DEFINE TPM2_ENABLE             = FALSE
   DEFINE TPM2_CONFIG_ENABLE      = FALSE
 
@@ -69,7 +70,7 @@
 !if $(TOOL_CHAIN_TAG) != "XCODE5"
   GCC:*_*_*_CC_FLAGS                   = -mno-mmx -mno-sse
 !endif
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   MSFT:*_*_X64_GENFW_FLAGS  = --keepexceptiontable
   GCC:*_*_X64_GENFW_FLAGS   = --keepexceptiontable
   INTEL:*_*_X64_GENFW_FLAGS = --keepexceptiontable
@@ -162,7 +163,7 @@
   CustomizedDisplayLib|MdeModulePkg/Library/CustomizedDisplayLib/CustomizedDisplayLib.inf
   FrameBufferBltLib|MdeModulePkg/Library/FrameBufferBltLib/FrameBufferBltLib.inf
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   PeCoffExtraActionLib|SourceLevelDebugPkg/Library/PeCoffExtraActionLibDebug/PeCoffExtraActionLibDebug.inf
   DebugCommunicationLib|SourceLevelDebugPkg/Library/DebugCommunicationLibSerialPort/DebugCommunicationLibSerialPort.inf
 !else
@@ -230,7 +231,7 @@
 !endif
   ReportStatusCodeLib|MdeModulePkg/Library/PeiReportStatusCodeLib/PeiReportStatusCodeLib.inf
   ExtractGuidedSectionLib|MdePkg/Library/BaseExtractGuidedSectionLib/BaseExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgentLib.inf
 !endif
   HobLib|MdePkg/Library/PeiHobLib/PeiHobLib.inf
@@ -272,7 +273,7 @@
   PeCoffLib|MdePkg/Library/BasePeCoffLib/BasePeCoffLib.inf
   ResourcePublicationLib|MdePkg/Library/PeiResourcePublicationLib/PeiResourcePublicationLib.inf
   ExtractGuidedSectionLib|MdePkg/Library/PeiExtractGuidedSectionLib/PeiExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgentLib.inf
 !endif
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuExceptionHandlerLib.inf
@@ -297,7 +298,7 @@
   DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
 !endif
   ExtractGuidedSectionLib|MdePkg/Library/DxeExtractGuidedSectionLib/DxeExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgentLib.inf
 !endif
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeCpuExceptionHandlerLib.inf
@@ -356,7 +357,7 @@
 !else
   LockBoxLib|OvmfPkg/Library/LockBoxLib/LockBoxDxeLib.inf
 !endif
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgentLib.inf
 !endif
   PciLib|OvmfPkg/Library/DxePciLibI440FxQ35/DxePciLibI440FxQ35.inf
@@ -394,7 +395,7 @@
   DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
 !endif
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/SmmCpuExceptionHandlerLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/SmmDebugAgentLib.inf
 !endif
   BaseCryptLib|CryptoPkg/Library/BaseCryptLib/SmmCryptLib.inf
@@ -486,7 +487,7 @@
   # DEBUG_ERROR     0x80000000  // Error
   gEfiMdePkgTokenSpaceGuid.PcdDebugPrintErrorLevel|0x8000004F
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask|0x17
 !else
   gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask|0x2F
@@ -500,7 +501,7 @@
   # never lets the RAM below 4 GB exceed 2816 MB.
   gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress|0xB0000000
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   gEfiSourceLevelDebugPkgTokenSpaceGuid.PcdDebugLoadImageMethod|0x2
 !endif
 
diff --git a/OvmfPkg/OvmfPkgIa32X64.fdf b/OvmfPkg/OvmfPkgIa32X64.fdf
index 7440707256..e49adc425f 100644
--- a/OvmfPkg/OvmfPkgIa32X64.fdf
+++ b/OvmfPkg/OvmfPkgIa32X64.fdf
@@ -261,7 +261,7 @@ INF  MdeModulePkg/Universal/DisplayEngineDxe/DisplayEngineDxe.inf
 INF  MdeModulePkg/Universal/MemoryTest/NullMemoryTestDxe/NullMemoryTestDxe.inf
 
 INF  OvmfPkg/SioBusDxe/SioBusDxe.inf
-!ifndef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == FALSE
 INF  MdeModulePkg/Bus/Pci/PciSioSerialDxe/PciSioSerialDxe.inf
 !endif
 INF  MdeModulePkg/Bus/Isa/Ps2KeyboardDxe/Ps2KeyboardDxe.inf
diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
index ba7a758844..5dbd1b793a 100644
--- a/OvmfPkg/OvmfPkgX64.dsc
+++ b/OvmfPkg/OvmfPkgX64.dsc
@@ -30,6 +30,7 @@
   #
   DEFINE SECURE_BOOT_ENABLE      = FALSE
   DEFINE SMM_REQUIRE             = FALSE
+  DEFINE SOURCE_DEBUG_ENABLE     = FALSE
   DEFINE TPM2_ENABLE             = FALSE
   DEFINE TPM2_CONFIG_ENABLE      = FALSE
 
@@ -69,7 +70,7 @@
 !if $(TOOL_CHAIN_TAG) != "XCODE5"
   GCC:*_*_*_CC_FLAGS                   = -mno-mmx -mno-sse
 !endif
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   MSFT:*_*_X64_GENFW_FLAGS  = --keepexceptiontable
   GCC:*_*_X64_GENFW_FLAGS   = --keepexceptiontable
   INTEL:*_*_X64_GENFW_FLAGS = --keepexceptiontable
@@ -162,7 +163,7 @@
   CustomizedDisplayLib|MdeModulePkg/Library/CustomizedDisplayLib/CustomizedDisplayLib.inf
   FrameBufferBltLib|MdeModulePkg/Library/FrameBufferBltLib/FrameBufferBltLib.inf
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   PeCoffExtraActionLib|SourceLevelDebugPkg/Library/PeCoffExtraActionLibDebug/PeCoffExtraActionLibDebug.inf
   DebugCommunicationLib|SourceLevelDebugPkg/Library/DebugCommunicationLibSerialPort/DebugCommunicationLibSerialPort.inf
 !else
@@ -230,7 +231,7 @@
 !endif
   ReportStatusCodeLib|MdeModulePkg/Library/PeiReportStatusCodeLib/PeiReportStatusCodeLib.inf
   ExtractGuidedSectionLib|MdePkg/Library/BaseExtractGuidedSectionLib/BaseExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgentLib.inf
 !endif
   HobLib|MdePkg/Library/PeiHobLib/PeiHobLib.inf
@@ -272,7 +273,7 @@
   PeCoffLib|MdePkg/Library/BasePeCoffLib/BasePeCoffLib.inf
   ResourcePublicationLib|MdePkg/Library/PeiResourcePublicationLib/PeiResourcePublicationLib.inf
   ExtractGuidedSectionLib|MdePkg/Library/PeiExtractGuidedSectionLib/PeiExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgentLib.inf
 !endif
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuExceptionHandlerLib.inf
@@ -297,7 +298,7 @@
   DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
 !endif
   ExtractGuidedSectionLib|MdePkg/Library/DxeExtractGuidedSectionLib/DxeExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgentLib.inf
 !endif
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeCpuExceptionHandlerLib.inf
@@ -356,7 +357,7 @@
 !else
   LockBoxLib|OvmfPkg/Library/LockBoxLib/LockBoxDxeLib.inf
 !endif
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgentLib.inf
 !endif
   PciLib|OvmfPkg/Library/DxePciLibI440FxQ35/DxePciLibI440FxQ35.inf
@@ -394,7 +395,7 @@
   DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
 !endif
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/SmmCpuExceptionHandlerLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/SmmDebugAgentLib.inf
 !endif
   BaseCryptLib|CryptoPkg/Library/BaseCryptLib/SmmCryptLib.inf
@@ -486,7 +487,7 @@
   # DEBUG_ERROR     0x80000000  // Error
   gEfiMdePkgTokenSpaceGuid.PcdDebugPrintErrorLevel|0x8000004F
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask|0x17
 !else
   gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask|0x2F
@@ -500,7 +501,7 @@
   # never lets the RAM below 4 GB exceed 2816 MB.
   gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress|0xB0000000
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   gEfiSourceLevelDebugPkgTokenSpaceGuid.PcdDebugLoadImageMethod|0x2
 !endif
 
diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
index 7440707256..e49adc425f 100644
--- a/OvmfPkg/OvmfPkgX64.fdf
+++ b/OvmfPkg/OvmfPkgX64.fdf
@@ -261,7 +261,7 @@ INF  MdeModulePkg/Universal/DisplayEngineDxe/DisplayEngineDxe.inf
 INF  MdeModulePkg/Universal/MemoryTest/NullMemoryTestDxe/NullMemoryTestDxe.inf
 
 INF  OvmfPkg/SioBusDxe/SioBusDxe.inf
-!ifndef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == FALSE
 INF  MdeModulePkg/Bus/Pci/PciSioSerialDxe/PciSioSerialDxe.inf
 !endif
 INF  MdeModulePkg/Bus/Isa/Ps2KeyboardDxe/Ps2KeyboardDxe.inf
diff --git a/OvmfPkg/OvmfXen.dsc b/OvmfPkg/OvmfXen.dsc
index 5a31f75f05..8c11efe9b7 100644
--- a/OvmfPkg/OvmfXen.dsc
+++ b/OvmfPkg/OvmfXen.dsc
@@ -29,6 +29,7 @@
   # Defines for default states.  These can be changed on the command line.
   # -D FLAG=VALUE
   #
+  DEFINE SOURCE_DEBUG_ENABLE     = FALSE
 
   #
   # Network definition
@@ -66,7 +67,7 @@
 !if $(TOOL_CHAIN_TAG) != "XCODE5"
   GCC:*_*_*_CC_FLAGS                   = -mno-mmx -mno-sse
 !endif
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   MSFT:*_*_X64_GENFW_FLAGS  = --keepexceptiontable
   GCC:*_*_X64_GENFW_FLAGS   = --keepexceptiontable
   INTEL:*_*_X64_GENFW_FLAGS = --keepexceptiontable
@@ -156,7 +157,7 @@
   CustomizedDisplayLib|MdeModulePkg/Library/CustomizedDisplayLib/CustomizedDisplayLib.inf
   FrameBufferBltLib|MdeModulePkg/Library/FrameBufferBltLib/FrameBufferBltLib.inf
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   PeCoffExtraActionLib|SourceLevelDebugPkg/Library/PeCoffExtraActionLibDebug/PeCoffExtraActionLibDebug.inf
   DebugCommunicationLib|SourceLevelDebugPkg/Library/DebugCommunicationLibSerialPort/DebugCommunicationLibSerialPort.inf
 !else
@@ -213,7 +214,7 @@
 !endif
   ReportStatusCodeLib|MdeModulePkg/Library/PeiReportStatusCodeLib/PeiReportStatusCodeLib.inf
   ExtractGuidedSectionLib|MdePkg/Library/BaseExtractGuidedSectionLib/BaseExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgentLib.inf
 !endif
   HobLib|MdePkg/Library/PeiHobLib/PeiHobLib.inf
@@ -255,7 +256,7 @@
   PeCoffLib|MdePkg/Library/BasePeCoffLib/BasePeCoffLib.inf
   ResourcePublicationLib|MdePkg/Library/PeiResourcePublicationLib/PeiResourcePublicationLib.inf
   ExtractGuidedSectionLib|MdePkg/Library/PeiExtractGuidedSectionLib/PeiExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgentLib.inf
 !endif
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuExceptionHandlerLib.inf
@@ -275,7 +276,7 @@
   DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
 !endif
   ExtractGuidedSectionLib|MdePkg/Library/DxeExtractGuidedSectionLib/DxeExtractGuidedSectionLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgentLib.inf
 !endif
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeCpuExceptionHandlerLib.inf
@@ -327,7 +328,7 @@
   QemuBootOrderLib|OvmfPkg/Library/QemuBootOrderLib/QemuBootOrderLib.inf
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeCpuExceptionHandlerLib.inf
   LockBoxLib|OvmfPkg/Library/LockBoxLib/LockBoxDxeLib.inf
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   DebugAgentLib|SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgentLib.inf
 !endif
   PciLib|OvmfPkg/Library/DxePciLibI440FxQ35/DxePciLibI440FxQ35.inf
@@ -412,7 +413,7 @@
   # DEBUG_ERROR     0x80000000  // Error
   gEfiMdePkgTokenSpaceGuid.PcdDebugPrintErrorLevel|0x8000004F
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask|0x17
 !else
   gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask|0x2F
@@ -426,7 +427,7 @@
   # never lets the RAM below 4 GB exceed 2816 MB.
   gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress|0xB0000000
 
-!ifdef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == TRUE
   gEfiSourceLevelDebugPkgTokenSpaceGuid.PcdDebugLoadImageMethod|0x2
 !endif
 
diff --git a/OvmfPkg/OvmfXen.fdf b/OvmfPkg/OvmfXen.fdf
index e6e9e184ef..05138ffc5b 100644
--- a/OvmfPkg/OvmfXen.fdf
+++ b/OvmfPkg/OvmfXen.fdf
@@ -343,7 +343,7 @@ INF  MdeModulePkg/Universal/DisplayEngineDxe/DisplayEngineDxe.inf
 INF  MdeModulePkg/Universal/MemoryTest/NullMemoryTestDxe/NullMemoryTestDxe.inf
 
 INF  OvmfPkg/SioBusDxe/SioBusDxe.inf
-!ifndef $(SOURCE_DEBUG_ENABLE)
+!if $(SOURCE_DEBUG_ENABLE) == FALSE
 INF  MdeModulePkg/Bus/Pci/PciSioSerialDxe/PciSioSerialDxe.inf
 !endif
 INF  MdeModulePkg/Bus/Isa/Ps2KeyboardDxe/Ps2KeyboardDxe.inf