diff --git a/ArmPkg/ArmPkg.dec b/ArmPkg/ArmPkg.dec
index 5e846c9cd2..df56e6326d 100644
--- a/ArmPkg/ArmPkg.dec
+++ b/ArmPkg/ArmPkg.dec
@@ -182,6 +182,11 @@
   gArmTokenSpaceGuid.PcdHypFvBaseAddress|0|UINT32|0x0000003C
   gArmTokenSpaceGuid.PcdHypFvSize|0|UINT32|0x0000003D
 
+  #
+  # ARM StanaloneMm Stack size.
+  #
+  gArmTokenSpaceGuid.PcdStMmStackSize|0x2000|UINT32|0x0000005D
+
   # Use ClusterId + CoreId to identify the PrimaryCore
   gArmTokenSpaceGuid.PcdArmPrimaryCoreMask|0xF03|UINT32|0x00000031
   # The Primary Core is ClusterId[0] & CoreId[0]