diff --git a/core/fpdfapi/page/cpdf_page.h b/core/fpdfapi/page/cpdf_page.h
index 32d8296..d2ff1ac 100644
--- a/core/fpdfapi/page/cpdf_page.h
+++ b/core/fpdfapi/page/cpdf_page.h
@@ -13,6 +13,7 @@
 #include "core/fpdfapi/page/cpdf_pageobjectholder.h"
 #include "core/fpdfapi/page/ipdf_page.h"
 #include "core/fxcrt/fx_coordinates.h"
+#include "core/fxcrt/fx_memory.h"
 #include "core/fxcrt/observed_ptr.h"
 #include "core/fxcrt/retain_ptr.h"
 #include "core/fxcrt/unowned_ptr.h"
@@ -43,6 +44,7 @@
 
   class RenderContextClearer {
    public:
+    FX_STACK_ALLOCATED();
     explicit RenderContextClearer(CPDF_Page* pPage);
     ~RenderContextClearer();
 
diff --git a/core/fpdfapi/parser/cpdf_array.h b/core/fpdfapi/parser/cpdf_array.h
index 6761a97..2270c7d 100644
--- a/core/fpdfapi/parser/cpdf_array.h
+++ b/core/fpdfapi/parser/cpdf_array.h
@@ -162,6 +162,7 @@
 
 class CPDF_ArrayLocker {
  public:
+  FX_STACK_ALLOCATED();
   using const_iterator = CPDF_Array::const_iterator;
 
   explicit CPDF_ArrayLocker(const CPDF_Array* pArray);
diff --git a/core/fpdfapi/parser/cpdf_dictionary.h b/core/fpdfapi/parser/cpdf_dictionary.h
index d8ba1c0..d2f8143 100644
--- a/core/fpdfapi/parser/cpdf_dictionary.h
+++ b/core/fpdfapi/parser/cpdf_dictionary.h
@@ -137,6 +137,7 @@
 
 class CPDF_DictionaryLocker {
  public:
+  FX_STACK_ALLOCATED();
   using const_iterator = CPDF_Dictionary::const_iterator;
 
   explicit CPDF_DictionaryLocker(const CPDF_Dictionary* pDictionary);
diff --git a/core/fxcrt/fx_memory.h b/core/fxcrt/fx_memory.h
index 8669123..d9bf9c9 100644
--- a/core/fxcrt/fx_memory.h
+++ b/core/fxcrt/fx_memory.h
@@ -89,7 +89,11 @@
 }  // namespace internal
 }  // namespace pdfium
 
-// Force stack allocation of a class.
+// Force stack allocation of a class. Classes that do complex work in a
+// destructor, such as the flushing of buffers, should be declared as
+// stack-allocated as possible, since future memory allocation schemes
+// may not run destructors in a predictable manner if an instance is
+// heap-allocated.
 #define FX_STACK_ALLOCATED()           \
   void* operator new(size_t) = delete; \
   void* operator new(size_t, void*) = delete