diff --git a/SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgent/DxeDebugAgentLib.c b/SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgent/DxeDebugAgentLib.c
index f7fbb3ccfa..35fb5e6450 100644
--- a/SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgent/DxeDebugAgentLib.c
+++ b/SourceLevelDebugPkg/Library/DebugAgent/DxeDebugAgent/DxeDebugAgentLib.c
@@ -512,7 +512,7 @@ InitializeDebugAgent (
       Ia32Idtr =  (IA32_DESCRIPTOR *) Context;
       Ia32IdtEntry = (IA32_IDT_ENTRY *)(Ia32Idtr->Base);
       MailboxLocation = (UINT64 *) (UINTN) (Ia32IdtEntry[DEBUG_MAILBOX_VECTOR].Bits.OffsetLow +
-                                           (Ia32IdtEntry[DEBUG_MAILBOX_VECTOR].Bits.OffsetHigh << 16));
+                                  (UINT32) (Ia32IdtEntry[DEBUG_MAILBOX_VECTOR].Bits.OffsetHigh << 16));
       Mailbox = (DEBUG_AGENT_MAILBOX *)(UINTN)(*MailboxLocation);
       VerifyMailboxChecksum (Mailbox);
     }
diff --git a/SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgent/SecPeiDebugAgentLib.c b/SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgent/SecPeiDebugAgentLib.c
index e77ff723e3..fcc7a4baf8 100644
--- a/SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgent/SecPeiDebugAgentLib.c
+++ b/SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgent/SecPeiDebugAgentLib.c
@@ -579,7 +579,7 @@ InitializeDebugAgent (
       Ia32Idtr =  (IA32_DESCRIPTOR *) Context;
       Ia32IdtEntry = (IA32_IDT_ENTRY *)(Ia32Idtr->Base);
       MailboxLocationPointer = (UINT64 *) (UINTN) (Ia32IdtEntry[DEBUG_MAILBOX_VECTOR].Bits.OffsetLow +
-                                                (Ia32IdtEntry[DEBUG_MAILBOX_VECTOR].Bits.OffsetHigh << 16));
+                                         (UINT32) (Ia32IdtEntry[DEBUG_MAILBOX_VECTOR].Bits.OffsetHigh << 16));
       Mailbox = (DEBUG_AGENT_MAILBOX *) (UINTN)(*MailboxLocationPointer);
       //
       // Mailbox should valid and setup before executing thunk code
diff --git a/SourceLevelDebugPkg/Library/DebugAgent/SmmDebugAgent/SmmDebugAgentLib.c b/SourceLevelDebugPkg/Library/DebugAgent/SmmDebugAgent/SmmDebugAgentLib.c
index 6ac5f88dea..3a759f900d 100644
--- a/SourceLevelDebugPkg/Library/DebugAgent/SmmDebugAgent/SmmDebugAgentLib.c
+++ b/SourceLevelDebugPkg/Library/DebugAgent/SmmDebugAgent/SmmDebugAgentLib.c
@@ -328,7 +328,7 @@ InitializeDebugAgent (
       Ia32Idtr =  (IA32_DESCRIPTOR *) Context;
       Ia32IdtEntry = (IA32_IDT_ENTRY *)(Ia32Idtr->Base);
       MailboxLocation = (UINT64 *) (UINTN) (Ia32IdtEntry[DEBUG_MAILBOX_VECTOR].Bits.OffsetLow + 
-                                           (Ia32IdtEntry[DEBUG_MAILBOX_VECTOR].Bits.OffsetHigh << 16));
+                                  (UINT32) (Ia32IdtEntry[DEBUG_MAILBOX_VECTOR].Bits.OffsetHigh << 16));
       mMailboxPointer = (DEBUG_AGENT_MAILBOX *)(UINTN)(*MailboxLocation);
       VerifyMailboxChecksum (mMailboxPointer);
       //