diff --git a/MdeModulePkg/Core/Dxe/Misc/MemoryAttributesTable.c b/MdeModulePkg/Core/Dxe/Misc/MemoryAttributesTable.c
index d39edb3417..6769f416f5 100644
--- a/MdeModulePkg/Core/Dxe/Misc/MemoryAttributesTable.c
+++ b/MdeModulePkg/Core/Dxe/Misc/MemoryAttributesTable.c
@@ -460,11 +460,17 @@ MergeMemoryMap (
   NewMemoryMapEntry = MemoryMap;
   MemoryMapEnd      = (EFI_MEMORY_DESCRIPTOR *)((UINT8 *)MemoryMap + *MemoryMapSize);
   while ((UINTN)MemoryMapEntry < (UINTN)MemoryMapEnd) {
-    CopyMem (NewMemoryMapEntry, MemoryMapEntry, sizeof (EFI_MEMORY_DESCRIPTOR));
+    CopyMem (NewMemoryMapEntry, MemoryMapEntry, DescriptorSize); // MU_CHANGE Use size parameter for consistency.
     NextMemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry, DescriptorSize);
 
     do {
-      MergeGuardPages (NewMemoryMapEntry, NextMemoryMapEntry->PhysicalStart);
+      // MU_CHANGE START Fix overflow in the MergeGuardPages call.
+      if ((UINTN)NextMemoryMapEntry < (UINTN)MemoryMapEnd) {
+        MergeGuardPages (NewMemoryMapEntry, NextMemoryMapEntry->PhysicalStart);
+      }
+
+      // MU_CHANGE END
+
       MemoryBlockLength = (UINT64)(EfiPagesToSize (NewMemoryMapEntry->NumberOfPages));
       if (((UINTN)NextMemoryMapEntry < (UINTN)MemoryMapEnd) &&
           (NewMemoryMapEntry->Type == NextMemoryMapEntry->Type) &&