diff --git a/class.c b/class.c
index 8cd96f6346..2e084d1a96 100644
--- a/class.c
+++ b/class.c
@@ -56,11 +56,11 @@ rb_class_subclass_add(VALUE super, VALUE klass)
 	head = RCLASS_EXT(super)->subclasses;
 	if (head) {
 	    entry->next = head;
-	    RCLASS_EXT(head->klass)->parent_subclasses = &entry->next;
+	    RCLASS_PARENT_SUBCLASSES(head->klass) = &entry->next;
 	}
 
 	RCLASS_EXT(super)->subclasses = entry;
-	RCLASS_EXT(klass)->parent_subclasses = &RCLASS_EXT(super)->subclasses;
+	RCLASS_PARENT_SUBCLASSES(klass) = &RCLASS_EXT(super)->subclasses;
     }
 }
 
@@ -88,17 +88,17 @@ rb_class_remove_from_super_subclasses(VALUE klass)
 {
     rb_subclass_entry_t *entry;
 
-    if (RCLASS_EXT(klass)->parent_subclasses) {
-	entry = *RCLASS_EXT(klass)->parent_subclasses;
+    if (RCLASS_PARENT_SUBCLASSES(klass)) {
+	entry = *RCLASS_PARENT_SUBCLASSES(klass);
 
-	*RCLASS_EXT(klass)->parent_subclasses = entry->next;
+	*RCLASS_PARENT_SUBCLASSES(klass) = entry->next;
 	if (entry->next) {
-	    RCLASS_EXT(entry->next->klass)->parent_subclasses = RCLASS_EXT(klass)->parent_subclasses;
+	    RCLASS_PARENT_SUBCLASSES(entry->next->klass) = RCLASS_PARENT_SUBCLASSES(klass);
 	}
 	xfree(entry);
     }
 
-    RCLASS_EXT(klass)->parent_subclasses = NULL;
+    RCLASS_PARENT_SUBCLASSES(klass) = NULL;
 }
 
 void
@@ -182,7 +182,7 @@ class_alloc(VALUE flags, VALUE klass)
       RCLASS_IV_INDEX_TBL(obj) = 0;
       RCLASS_SET_SUPER((VALUE)obj, 0);
       RCLASS_EXT(obj)->subclasses = NULL;
-      RCLASS_EXT(obj)->parent_subclasses = NULL;
+      RCLASS_PARENT_SUBCLASSES(obj) = NULL;
       RCLASS_EXT(obj)->module_subclasses = NULL;
      */
     RCLASS_SET_ORIGIN((VALUE)obj, (VALUE)obj);
diff --git a/internal/class.h b/internal/class.h
index eade920ff0..da1df196be 100644
--- a/internal/class.h
+++ b/internal/class.h
@@ -92,6 +92,7 @@ typedef struct rb_classext_struct rb_classext_t;
 # define RCLASS_SERIAL(c) (RCLASS_EXT(c)->class_serial)
 #endif
 #define RCLASS_INCLUDER(c) (RCLASS_EXT(c)->includer)
+#define RCLASS_PARENT_SUBCLASSES(c) (RCLASS_EXT(c)->parent_subclasses)
 
 #define RICLASS_IS_ORIGIN FL_USER5
 #define RCLASS_CLONED     FL_USER6