diff --git a/runtime/caml/address_class.h b/runtime/caml/address_class.h
index 9f61008267..08403e2dda 100644
--- a/runtime/caml/address_class.h
+++ b/runtime/caml/address_class.h
@@ -15,44 +15,25 @@
 
 /* Classification of addresses for GC and runtime purposes. */
 
-/* The current runtime supports two different configurations that
-   correspond to two different value models, depending on whether
-   "naked pointers", that do not point to a well-formed OCaml block,
-   are allowed (considered valid values).
+/* Multicore runtime supports only the "no naked pointers" mode where any
+   out-of-heap pointers are not observable by the GC. The out-of-heap pointers
+   are either:
 
-   In "classic mode", naked pointers are allowed, and the
-   implementation uses a page table. A valid value is then either:
-   - a tagged integer (Is_long or !Is_block from mlvalues.h)
-   - a pointer to the minor heap (Is_young)
-   - a pointer to the major heap (Is_in_heap)
-   - a pointer to a constant block statically-allocated by OCaml code
-     or the OCaml runtime (Is_in_static_data)
-   - a "foreign" pointer, which is none of the above; the destination
-     of those pointers may be a well-formed OCaml blocks, but it may
-     also be a naked pointer.
+   - wrapped in Abstract_tag or Custom_tag objects, or
+   - have a valid header with colour `NOT_MARKABLE`, or
+   - made to look like immediate values by tagging the least significant bit so
+     that the GC does not follow it. This strategy has the downside that
+     out-of-heap pointers may not point to odd addresses.
 
-   The macros and functions below give access to a global page table
-   to classify addresses to be able to implement Is_in_heap,
-   In_static_data (or their disjunction Is_in_value_area) and thus
-   detect values which may be naked pointers. The runtime
-   conservatively assumes that all foreign pointers may be naked
-   pointers, and uses the page table to not dereference/follow them.
-
-   In "no naked pointers" mode (when NO_NAKED_POINTERS is defined),
-   naked pointers are illegal, so pointers that are values can always
-   be assumed to point to well-formed blocks.
-
-   To support an implementation without a global page table, runtime
-   code should not rely on Is_in_heap and Is_in_static_data. This
-   corresponds to a simpler model where a valid value is either:
+   A valid value is either:
    - a tagged integer (Is_long)
-   - a pointer to the minor heap (Is_young)
-   - a pointer to a well-formed block outside the minor heap
-     (it may be in the major heap, or static, or a foreign pointer,
-      without a check to distinguish the various cases).
+   - a pointer to the minor heap
+   - a pointer to a well-formed block outside the minor heap. It may be in the
+     major heap, or static data allocated by the OCaml code or the OCaml
+     runtime, or a foreign pointer.
 
-   (To create a well-formed block outside the heap that the GC will
-   not scan, one can use the Caml_out_of_heap_header from mlvalues.h.)
+   To create a well-formed block outside the heap that the GC will not scan,
+   one can use the Caml_out_of_heap_header from mlvalues.h.
 */
 
 #ifndef CAML_ADDRESS_CLASS_H
@@ -62,60 +43,8 @@
 #include "misc.h"
 #include "mlvalues.h"
 
-/* Use the following macros to test an address for the different classes
-   it might belong to. */
-
-#define Is_in_heap(a) (Classify_addr(a) & In_heap)
-
-#ifdef NO_NAKED_POINTERS
-
+/* These definitions are retained for backwards compatibility */
 #define Is_in_heap_or_young(a) 1
 #define Is_in_value_area(a) 1
 
-#else
-
-#define Is_in_heap_or_young(a) (Classify_addr(a) & (In_heap | In_young))
-
-#define Is_in_value_area(a)                                     \
-  (Classify_addr(a) & (In_heap | In_young | In_static_data))
-
-#define Is_in_static_data(a) (Classify_addr(a) & In_static_data)
-
-#endif
-
-/***********************************************************************/
-/* The rest of this file is private and may change without notice. */
-
-#define Not_in_heap 0
-#define In_heap 1
-#define In_young 2
-#define In_static_data 4
-
-#ifdef ARCH_SIXTYFOUR
-
-/* 64 bits: Represent page table as a sparse hash table */
-int caml_page_table_lookup(void * addr);
-#define Classify_addr(a) (caml_page_table_lookup((void *)(a)))
-
-#else
-
-/* 32 bits: Represent page table as a 2-level array */
-#define Pagetable2_log 11
-#define Pagetable2_size (1 << Pagetable2_log)
-#define Pagetable1_log (Page_log + Pagetable2_log)
-#define Pagetable1_size (1 << (32 - Pagetable1_log))
-CAMLextern unsigned char * caml_page_table[Pagetable1_size];
-
-#define Pagetable_index1(a) (((uintnat)(a)) >> Pagetable1_log)
-#define Pagetable_index2(a) \
-  ((((uintnat)(a)) >> Page_log) & (Pagetable2_size - 1))
-#define Classify_addr(a) \
-  caml_page_table[Pagetable_index1(a)][Pagetable_index2(a)]
-
-#endif
-
-int caml_page_table_add(int kind, void * start, void * end);
-int caml_page_table_remove(int kind, void * start, void * end);
-int caml_page_table_initialize(mlsize_t bytesize);
-
 #endif /* CAML_ADDRESS_CLASS_H */
diff --git a/runtime/caml/mlvalues.h b/runtime/caml/mlvalues.h
index 4412c30377..640f689670 100644
--- a/runtime/caml/mlvalues.h
+++ b/runtime/caml/mlvalues.h
@@ -443,6 +443,14 @@ Caml_inline void caml_read_field(value x, intnat i, value* ret) {
 #define Long_field(x, i) Long_val(Field(x, i))
 #define Bool_field(x, i) Bool_val(Field(x, i))
 
+/* Header for out-of-heap blocks. */
+
+#define Caml_out_of_heap_header(wosize, tag)                                  \
+      (/*CAMLassert ((wosize) <= Max_wosize),*/                               \
+       ((header_t) (((header_t) (wosize) << 10)                               \
+           + (3 << 8) /* matches [NOT_MARKABLE]. See [shared_heap.h]. */      \
+           + (tag_t) (tag)))                                                  \
+      )
 
 #ifdef __cplusplus
 }