diff --git a/app/core/gimpfilter.c b/app/core/gimpfilter.c
index 1696ff8546..35035b3a0f 100644
--- a/app/core/gimpfilter.c
+++ b/app/core/gimpfilter.c
@@ -57,7 +57,8 @@ struct _GimpFilterPrivate
   GimpApplicator *applicator;
 };
 
-#define GET_PRIVATE(filter) ((GimpFilterPrivate *) gimp_filter_get_instance_private ((GimpFilter *) (filter)))
+#define GET_PRIVATE(filter) \
+  ((GimpFilterPrivate *) gimp_filter_get_instance_private ((GimpFilter *) (filter)))
 
 
 /*  local function prototypes  */
@@ -223,12 +224,10 @@ gimp_filter_new (const gchar *name)
 GeglNode *
 gimp_filter_get_node (GimpFilter *filter)
 {
-  GimpFilterPrivate *private;
+  GimpFilterPrivate *private = GET_PRIVATE (filter);
 
   g_return_val_if_fail (GIMP_IS_FILTER (filter), NULL);
 
-  private = GET_PRIVATE (filter);
-
   if (private->node)
     return private->node;
 
@@ -297,12 +296,10 @@ void
 gimp_filter_set_applicator (GimpFilter     *filter,
                             GimpApplicator *applicator)
 {
-  GimpFilterPrivate *private;
+  GimpFilterPrivate *private = GET_PRIVATE (filter);
 
   g_return_if_fail (GIMP_IS_FILTER (filter));
 
-  private = GET_PRIVATE (filter);
-
   private->applicator = applicator;
 }
 
diff --git a/app/core/gimpfilter.h b/app/core/gimpfilter.h
index b1dc9225ed..c1272894b0 100644
--- a/app/core/gimpfilter.h
+++ b/app/core/gimpfilter.h
@@ -24,21 +24,13 @@
 #include "gimpviewable.h"
 
 
-#define GIMP_TYPE_FILTER            (gimp_filter_get_type ())
-#define GIMP_FILTER(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), GIMP_TYPE_FILTER, GimpFilter))
-#define GIMP_FILTER_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GIMP_TYPE_FILTER, GimpFilterClass))
-#define GIMP_IS_FILTER(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GIMP_TYPE_FILTER))
-#define GIMP_IS_FILTER_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GIMP_TYPE_FILTER))
-#define GIMP_FILTER_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), GIMP_TYPE_FILTER, GimpFilterClass))
+#define GIMP_TYPE_FILTER (gimp_filter_get_type ())
+G_DECLARE_DERIVABLE_TYPE (GimpFilter,
+                          gimp_filter,
+                          GIMP, FILTER,
+                          GimpViewable)
 
 
-typedef struct _GimpFilterClass GimpFilterClass;
-
-struct _GimpFilter
-{
-  GimpViewable  parent_instance;
-};
-
 struct _GimpFilterClass
 {
   GimpViewableClass  parent_class;
diff --git a/app/core/gimpitem.h b/app/core/gimpitem.h
index 2be9a355bf..90179da585 100644
--- a/app/core/gimpitem.h
+++ b/app/core/gimpitem.h
@@ -22,21 +22,13 @@
 #include "gimpfilter.h"
 
 
-#define GIMP_TYPE_ITEM            (gimp_item_get_type ())
-#define GIMP_ITEM(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), GIMP_TYPE_ITEM, GimpItem))
-#define GIMP_ITEM_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GIMP_TYPE_ITEM, GimpItemClass))
-#define GIMP_IS_ITEM(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GIMP_TYPE_ITEM))
-#define GIMP_IS_ITEM_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GIMP_TYPE_ITEM))
-#define GIMP_ITEM_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), GIMP_TYPE_ITEM, GimpItemClass))
+#define GIMP_TYPE_ITEM (gimp_item_get_type ())
+G_DECLARE_DERIVABLE_TYPE (GimpItem,
+                          gimp_item,
+                          GIMP, ITEM,
+                          GimpFilter)
 
 
-typedef struct _GimpItemClass GimpItemClass;
-
-struct _GimpItem
-{
-  GimpFilter  parent_instance;
-};
-
 struct _GimpItemClass
 {
   GimpFilterClass  parent_class;
diff --git a/app/core/gimpviewable.c b/app/core/gimpviewable.c
index 890cda9fea..c7225c7d9a 100644
--- a/app/core/gimpviewable.c
+++ b/app/core/gimpviewable.c
@@ -48,8 +48,10 @@ enum
   PROP_FROZEN,
   N_PROPS
 };
+
 static GParamSpec *obj_props[N_PROPS] = { NULL, };
 
+
 enum
 {
   INVALIDATE_PREVIEW,
@@ -80,7 +82,8 @@ struct _GimpViewablePrivate
   GeglColor    *preview_temp_buf_background;
 };
 
-#define GET_PRIVATE(viewable) ((GimpViewablePrivate *) gimp_viewable_get_instance_private ((GimpViewable *) (viewable)))
+#define GET_PRIVATE(viewable) \
+  ((GimpViewablePrivate *) gimp_viewable_get_instance_private ((GimpViewable *) (viewable)))
 
 
 static void    gimp_viewable_config_iface_init (GimpConfigInterface *iface);
@@ -583,7 +586,6 @@ gimp_viewable_invalidate_preview (GimpViewable *viewable)
 
   g_return_if_fail (GIMP_IS_VIEWABLE (viewable));
 
-
   if (private->freeze_count == 0)
     g_signal_emit (viewable, viewable_signals[INVALIDATE_PREVIEW], 0);
   else
diff --git a/app/core/gimpviewable.h b/app/core/gimpviewable.h
index 238810a583..bbcfeb4343 100644
--- a/app/core/gimpviewable.h
+++ b/app/core/gimpviewable.h
@@ -31,21 +31,13 @@
 #define GIMP_VIEWABLE_MAX_MENU_SIZE      48
 
 
-#define GIMP_TYPE_VIEWABLE            (gimp_viewable_get_type ())
-#define GIMP_VIEWABLE(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), GIMP_TYPE_VIEWABLE, GimpViewable))
-#define GIMP_VIEWABLE_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GIMP_TYPE_VIEWABLE, GimpViewableClass))
-#define GIMP_IS_VIEWABLE(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GIMP_TYPE_VIEWABLE))
-#define GIMP_IS_VIEWABLE_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GIMP_TYPE_VIEWABLE))
-#define GIMP_VIEWABLE_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), GIMP_TYPE_VIEWABLE, GimpViewableClass))
+#define GIMP_TYPE_VIEWABLE (gimp_viewable_get_type ())
+G_DECLARE_DERIVABLE_TYPE (GimpViewable,
+                          gimp_viewable,
+                          GIMP, VIEWABLE,
+                          GimpObject)
 
 
-typedef struct _GimpViewableClass GimpViewableClass;
-
-struct _GimpViewable
-{
-  GimpObject  parent_instance;
-};
-
 struct _GimpViewableClass
 {
   GimpObjectClass  parent_class;
@@ -213,7 +205,5 @@ void            gimp_viewable_set_expanded       (GimpViewable  *viewable,
 gboolean        gimp_viewable_is_ancestor        (GimpViewable  *ancestor,
                                                   GimpViewable  *descendant);
 
-G_DEFINE_AUTOPTR_CLEANUP_FUNC (GimpViewable, g_object_unref);
-
 
 #endif  /* __GIMP_VIEWABLE_H__ */