diff --git a/cont.c b/cont.c
index 463be7400f..8af093a316 100644
--- a/cont.c
+++ b/cont.c
@@ -48,8 +48,8 @@ static const int DEBUG = 0;
 #define RB_PAGE_MASK (~(RB_PAGE_SIZE - 1))
 static long pagesize;
 
-const rb_data_type_t rb_cont_data_type;
-const rb_data_type_t rb_fiber_data_type;
+static const rb_data_type_t rb_cont_data_type;
+static const rb_data_type_t rb_fiber_data_type;
 static VALUE rb_cContinuation;
 static VALUE rb_cFiber;
 static VALUE rb_eFiberError;
@@ -1239,17 +1239,11 @@ cont_save_machine_stack(rb_thread_t *th, rb_context_t *cont)
     asan_unpoison_memory_region(cont->machine.stack_src, size, false);
     MEMCPY(cont->machine.stack, cont->machine.stack_src, VALUE, size);
 }
-const rb_data_type_t rb_cont_data_type = {
-    "continuation",
-    {cont_mark, cont_free, cont_memsize, cont_compact},
-    0, 0, RUBY_TYPED_FREE_IMMEDIATELY
-};
 
-void
-rb_cont_handle_weak_references(VALUE obj)
+static void
+cont_handle_weak_references(void *ptr)
 {
-    rb_context_t *cont;
-    TypedData_Get_Struct(obj, rb_context_t, &rb_cont_data_type, cont);
+    rb_context_t *cont = ptr;
 
     if (!cont) return;
 
@@ -1260,6 +1254,12 @@ rb_cont_handle_weak_references(VALUE obj)
     }
 }
 
+static const rb_data_type_t rb_cont_data_type = {
+    "continuation",
+    {cont_mark, cont_free, cont_memsize, cont_compact, cont_handle_weak_references},
+    0, 0, RUBY_TYPED_FREE_IMMEDIATELY
+};
+
 static inline void
 cont_save_thread(rb_context_t *cont, rb_thread_t *th)
 {
@@ -1996,17 +1996,10 @@ rb_cont_call(int argc, VALUE *argv, VALUE contval)
  *
  */
 
-const rb_data_type_t rb_fiber_data_type = {
-    "fiber",
-    {fiber_mark, fiber_free, fiber_memsize, fiber_compact,},
-    0, 0, RUBY_TYPED_FREE_IMMEDIATELY
-};
-
-void
-rb_fiber_handle_weak_references(VALUE obj)
+static void
+fiber_handle_weak_references(void *ptr)
 {
-    rb_fiber_t *fiber;
-    TypedData_Get_Struct(obj, rb_fiber_t, &rb_fiber_data_type, fiber);
+    rb_fiber_t *fiber = ptr;
 
     if (!fiber) return;
 
@@ -2017,6 +2010,12 @@ rb_fiber_handle_weak_references(VALUE obj)
     }
 }
 
+static const rb_data_type_t rb_fiber_data_type = {
+    "fiber",
+    {fiber_mark, fiber_free, fiber_memsize, fiber_compact, fiber_handle_weak_references},
+    0, 0, RUBY_TYPED_FREE_IMMEDIATELY
+};
+
 static VALUE
 fiber_alloc(VALUE klass)
 {
diff --git a/gc.c b/gc.c
index 98e5712ca4..c47f68c50c 100644
--- a/gc.c
+++ b/gc.c
@@ -1204,17 +1204,6 @@ rb_gc_handle_weak_references_alive_p(VALUE obj)
     return rb_gc_impl_handle_weak_references_alive_p(rb_gc_get_objspace(), obj);
 }
 
-extern const rb_data_type_t rb_weakmap_type;
-void rb_wmap_handle_weak_references(VALUE obj);
-extern const rb_data_type_t rb_weakkeymap_type;
-void rb_wkmap_handle_weak_references(VALUE obj);
-
-extern const rb_data_type_t rb_fiber_data_type;
-void rb_fiber_handle_weak_references(VALUE obj);
-
-extern const rb_data_type_t rb_cont_data_type;
-void rb_cont_handle_weak_references(VALUE obj);
-
 void
 rb_gc_handle_weak_references(VALUE obj)
 {
@@ -1223,20 +1212,14 @@ rb_gc_handle_weak_references(VALUE obj)
         if (RTYPEDDATA_P(obj)) {
             const rb_data_type_t *type = RTYPEDDATA_TYPE(obj);
 
-            if (type == &rb_fiber_data_type) {
-                rb_fiber_handle_weak_references(obj);
-            }
-            else if (type == &rb_cont_data_type) {
-                rb_cont_handle_weak_references(obj);
-            }
-            else if (type == &rb_weakmap_type) {
-                rb_wmap_handle_weak_references(obj);
-            }
-            else if (type == &rb_weakkeymap_type) {
-                rb_wkmap_handle_weak_references(obj);
+            if (type->function.handle_weak_references) {
+                (type->function.handle_weak_references)(RTYPEDDATA_GET_DATA(obj));
             }
             else {
-                rb_bug("rb_gc_handle_weak_references: unknown TypedData %s", RTYPEDDATA_TYPE(obj)->wrap_struct_name);
+                rb_bug(
+                    "rb_gc_handle_weak_references: TypedData %s does not implement handle_weak_references",
+                    RTYPEDDATA_TYPE(obj)->wrap_struct_name
+                );
             }
         }
         else {
diff --git a/include/ruby/internal/core/rtypeddata.h b/include/ruby/internal/core/rtypeddata.h
index aadccc238b..bf6423f8d2 100644
--- a/include/ruby/internal/core/rtypeddata.h
+++ b/include/ruby/internal/core/rtypeddata.h
@@ -262,11 +262,9 @@ struct rb_data_type_struct {
         RUBY_DATA_FUNC dcompact;
 
         /**
-         * This field  is reserved for future  extension.  For now, it  must be
-         * filled with zeros.
+         * @internal
          */
-        void *reserved[1]; /* For future extension.
-                              This array *must* be filled with ZERO. */
+        void (*handle_weak_references)(void *);
     } function;
 
     /**
diff --git a/weakmap.c b/weakmap.c
index 7b6f27ce2b..b027604f5e 100644
--- a/weakmap.c
+++ b/weakmap.c
@@ -112,6 +112,26 @@ wmap_compact(void *ptr)
     }
 }
 
+static int
+rb_wmap_handle_weak_references_i(st_data_t key, st_data_t val, st_data_t arg)
+{
+    if (rb_gc_handle_weak_references_alive_p(key) &&
+            rb_gc_handle_weak_references_alive_p(val)) {
+        return ST_CONTINUE;
+    }
+    else {
+        return ST_DELETE;
+    }
+}
+
+static void
+wmap_handle_weak_references(void *ptr)
+{
+    struct weakmap *w = ptr;
+
+    st_foreach(w->table, rb_wmap_handle_weak_references_i, (st_data_t)0);
+}
+
 const rb_data_type_t rb_weakmap_type = {
     "weakmap",
     {
@@ -119,6 +139,7 @@ const rb_data_type_t rb_weakmap_type = {
         wmap_free,
         wmap_memsize,
         wmap_compact,
+        wmap_handle_weak_references,
     },
     0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED | RUBY_TYPED_EMBEDDABLE
 };
@@ -140,27 +161,6 @@ static const struct st_hash_type wmap_hash_type = {
     wmap_hash,
 };
 
-static int
-rb_wmap_handle_weak_references_i(st_data_t key, st_data_t val, st_data_t arg)
-{
-    if (rb_gc_handle_weak_references_alive_p(key) &&
-            rb_gc_handle_weak_references_alive_p(val)) {
-        return ST_CONTINUE;
-    }
-    else {
-        return ST_DELETE;
-    }
-}
-
-void
-rb_wmap_handle_weak_references(VALUE self)
-{
-    struct weakmap *w;
-    TypedData_Get_Struct(self, struct weakmap, &rb_weakmap_type, w);
-
-    st_foreach(w->table, rb_wmap_handle_weak_references_i, (st_data_t)0);
-}
-
 static VALUE
 wmap_allocate(VALUE klass)
 {
@@ -588,13 +588,33 @@ wkmap_compact(void *ptr)
     }
 }
 
-const rb_data_type_t rb_weakkeymap_type = {
+static int
+rb_wkmap_handle_weak_references_i(st_data_t key, st_data_t val, st_data_t arg)
+{
+    if (rb_gc_handle_weak_references_alive_p(key)) {
+        return ST_CONTINUE;
+    }
+    else {
+        return ST_DELETE;
+    }
+}
+
+static void
+wkmap_handle_weak_references(void *ptr)
+{
+    struct weakkeymap *w = ptr;
+
+    st_foreach(w->table, rb_wkmap_handle_weak_references_i, (st_data_t)0);
+}
+
+static const rb_data_type_t rb_weakkeymap_type = {
     "weakkeymap",
     {
         wkmap_mark,
         wkmap_free,
         wkmap_memsize,
         wkmap_compact,
+        wkmap_handle_weak_references,
     },
     0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED | RUBY_TYPED_EMBEDDABLE
 };
@@ -621,26 +641,6 @@ static const struct st_hash_type wkmap_hash_type = {
     wkmap_hash,
 };
 
-static int
-rb_wkmap_handle_weak_references_i(st_data_t key, st_data_t val, st_data_t arg)
-{
-    if (rb_gc_handle_weak_references_alive_p(key)) {
-        return ST_CONTINUE;
-    }
-    else {
-        return ST_DELETE;
-    }
-}
-
-void
-rb_wkmap_handle_weak_references(VALUE self)
-{
-    struct weakkeymap *w;
-    TypedData_Get_Struct(self, struct weakkeymap, &rb_weakkeymap_type, w);
-
-    st_foreach(w->table, rb_wkmap_handle_weak_references_i, (st_data_t)0);
-}
-
 static VALUE
 wkmap_allocate(VALUE klass)
 {