diff --git a/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c b/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c
index 19245049c2..ac043b5d9b 100644
--- a/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c
+++ b/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c
@@ -225,8 +225,8 @@ FindGuardedMemoryMap (
   //
   // Adjust current map table depth according to the address to access
   //
-  while (mMapLevel < GUARDED_HEAP_MAP_TABLE_DEPTH
-         &&
+  while (AllocMapUnit &&
+         mMapLevel < GUARDED_HEAP_MAP_TABLE_DEPTH &&
          RShiftU64 (
            Address,
            mLevelShift[GUARDED_HEAP_MAP_TABLE_DEPTH - mMapLevel - 1]
@@ -904,6 +904,10 @@ AdjustMemoryS (
   }
 
   Target = Start + Size - SizeRequested;
+  ASSERT (Target >= Start);
+  if (Target == 0) {
+    return 0;
+  }
 
   if (!IsGuardPage (Start + Size)) {
     // No Guard at tail to share. One more page is needed.