diff --git a/variable.c b/variable.c
index 1d2c6362c2..692d158a8c 100644
--- a/variable.c
+++ b/variable.c
@@ -2212,7 +2212,7 @@ autoload_data_memsize(const void *ptr)
 static const rb_data_type_t autoload_data_type = {
     "autoload_data",
     {autoload_data_mark, autoload_data_free, autoload_data_memsize, autoload_data_compact},
-    0, 0, RUBY_TYPED_FREE_IMMEDIATELY
+    0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED
 };
 
 static void
@@ -2263,11 +2263,12 @@ get_autoload_data(VALUE autoload_const_value, struct autoload_const **autoload_c
 {
     struct autoload_const *autoload_const = rb_check_typeddata(autoload_const_value, &autoload_const_type);
 
-    struct autoload_data *autoload_data = rb_check_typeddata(autoload_const->autoload_data_value, &autoload_data_type);
+    VALUE autoload_data_value = autoload_const->autoload_data_value;
+    struct autoload_data *autoload_data = rb_check_typeddata(autoload_data_value, &autoload_data_type);
 
     /* do not reach across stack for ->state after forking: */
     if (autoload_data && autoload_data->fork_gen != GET_VM()->fork_gen) {
-        autoload_data->mutex = Qnil;
+        RB_OBJ_WRITE(autoload_data_value, &autoload_data->mutex, Qnil);
         autoload_data->fork_gen = 0;
     }
 
@@ -2306,8 +2307,8 @@ autoload_feature_lookup_or_create(VALUE feature, struct autoload_data **autoload
 
     if (NIL_P(autoload_data_value)) {
         autoload_data_value = TypedData_Make_Struct(0, struct autoload_data, &autoload_data_type, autoload_data);
-        autoload_data->feature = feature;
-        autoload_data->mutex = Qnil;
+        RB_OBJ_WRITE(autoload_data_value, &autoload_data->feature, feature);
+        RB_OBJ_WRITE(autoload_data_value, &autoload_data->mutex, Qnil);
         ccan_list_head_init(&autoload_data->constants);
 
         if (autoload_data_pointer) *autoload_data_pointer = autoload_data;
@@ -2608,7 +2609,7 @@ autoload_load_needed(VALUE _arguments)
     }
 
     if (NIL_P(autoload_data->mutex)) {
-        autoload_data->mutex = rb_mutex_new();
+        RB_OBJ_WRITE(autoload_const->autoload_data_value, &autoload_data->mutex, rb_mutex_new());
         autoload_data->fork_gen = GET_VM()->fork_gen;
     }
     else if (rb_mutex_owned_p(autoload_data->mutex)) {