diff --git a/StandaloneMmPkg/Core/Mmi.c b/StandaloneMmPkg/Core/Mmi.c
index c1a1d76e85..9e52072bf7 100644
--- a/StandaloneMmPkg/Core/Mmi.c
+++ b/StandaloneMmPkg/Core/Mmi.c
@@ -36,8 +36,9 @@ typedef struct {
   MMI_ENTRY                     *MmiEntry;
 } MMI_HANDLER;
 
-LIST_ENTRY  mRootMmiHandlerList = INITIALIZE_LIST_HEAD_VARIABLE (mRootMmiHandlerList);
-LIST_ENTRY  mMmiEntryList       = INITIALIZE_LIST_HEAD_VARIABLE (mMmiEntryList);
+LIST_ENTRY   mRootMmiHandlerList = INITIALIZE_LIST_HEAD_VARIABLE (mRootMmiHandlerList);
+LIST_ENTRY   mMmiEntryList       = INITIALIZE_LIST_HEAD_VARIABLE (mMmiEntryList);
+MMI_HANDLER  *mCurrentMmiHandler = NULL;
 
 /**
   Finds the MMI entry for the requested handler type.
@@ -161,13 +162,19 @@ MmiManage (
     // get next node before handler is executed, since LIST_ENTRY that
     // Link points to may be freed if unregister MMI handler.
     //
-    Link   = Link->ForwardLink;
-    Status = MmiHandler->Handler (
-                           (EFI_HANDLE)MmiHandler,
-                           Context,
-                           CommBuffer,
-                           CommBufferSize
-                           );
+    Link = Link->ForwardLink;
+    //
+    // Assign gCurrentMmiHandle before calling the MMI handler and
+    // set to NULL when it returns.
+    //
+    mCurrentMmiHandler = MmiHandler;
+    Status             = MmiHandler->Handler (
+                                       (EFI_HANDLE)MmiHandler,
+                                       Context,
+                                       CommBuffer,
+                                       CommBufferSize
+                                       );
+    mCurrentMmiHandler = NULL;
 
     switch (Status) {
       case EFI_INTERRUPT_PENDING:
@@ -314,6 +321,13 @@ MmiHandlerUnRegister (
     return EFI_INVALID_PARAMETER;
   }
 
+  //
+  // Do not allow to unregister MMI Handler inside other MMI Handler
+  //
+  if ((mCurrentMmiHandler != NULL) && (mCurrentMmiHandler != MmiHandler)) {
+    return EFI_INVALID_PARAMETER;
+  }
+
   MmiEntry = MmiHandler->MmiEntry;
 
   RemoveEntryList (&MmiHandler->Link);