diff --git a/libgimp/gimppdb-private.h b/libgimp/gimppdb-private.h
index baf2baee9d..e0d66fddcd 100644
--- a/libgimp/gimppdb-private.h
+++ b/libgimp/gimppdb-private.h
@@ -41,14 +41,15 @@ typedef enum
 GQuark _gimp_pdb_error_quark (void) G_GNUC_CONST;
 
 
-GimpPDB    * _gimp_pdb_new         (GimpPlugIn   *plug_in);
+G_GNUC_INTERNAL GimpPDB        * _gimp_pdb_new                 (GimpPlugIn            *plug_in);
 
-GimpPlugIn * _gimp_pdb_get_plug_in (GimpPDB      *pdb);
+G_GNUC_INTERNAL GimpPlugIn     * _gimp_pdb_get_plug_in         (GimpPDB               *pdb);
+
+gboolean                         gimp_pdb_get_data             (const gchar           *identifier,
+                                                                GBytes               **data);
+gboolean                         gimp_pdb_set_data             (const gchar           *identifier,
+                                                                GBytes                *data);
 
-gboolean     gimp_pdb_get_data     (const gchar  *identifier,
-                                    GBytes      **data);
-gboolean     gimp_pdb_set_data     (const gchar  *identifier,
-                                    GBytes       *data);
 
 G_END_DECLS
 
diff --git a/libgimp/gimppixbuf.h b/libgimp/gimppixbuf.h
index 87646bee52..32722559a3 100644
--- a/libgimp/gimppixbuf.h
+++ b/libgimp/gimppixbuf.h
@@ -31,11 +31,11 @@ G_BEGIN_DECLS
 /* For information look into the C source or the html documentation */
 
 
-GdkPixbuf * _gimp_pixbuf_from_data (guchar                 *data,
-                                    gint                    width,
-                                    gint                    height,
-                                    gint                    bpp,
-                                    GimpPixbufTransparency  alpha);
+G_GNUC_INTERNAL GdkPixbuf * _gimp_pixbuf_from_data (guchar                 *data,
+                                                    gint                    width,
+                                                    gint                    height,
+                                                    gint                    bpp,
+                                                    GimpPixbufTransparency  alpha);
 
 
 G_END_DECLS
diff --git a/libgimp/gimpplugin-private.h b/libgimp/gimpplugin-private.h
index c418260718..b6be7431ee 100644
--- a/libgimp/gimpplugin-private.h
+++ b/libgimp/gimpplugin-private.h
@@ -25,38 +25,38 @@
 G_BEGIN_DECLS
 
 
-void            _gimp_plug_in_query                  (GimpPlugIn      *plug_in);
-void            _gimp_plug_in_init                   (GimpPlugIn      *plug_in);
-void            _gimp_plug_in_run                    (GimpPlugIn      *plug_in);
-void            _gimp_plug_in_quit                   (GimpPlugIn      *plug_in);
+G_GNUC_INTERNAL void            _gimp_plug_in_query                  (GimpPlugIn      *plug_in);
+G_GNUC_INTERNAL void            _gimp_plug_in_init                   (GimpPlugIn      *plug_in);
+G_GNUC_INTERNAL void            _gimp_plug_in_run                    (GimpPlugIn      *plug_in);
+G_GNUC_INTERNAL void            _gimp_plug_in_quit                   (GimpPlugIn      *plug_in);
 
-GIOChannel    * _gimp_plug_in_get_read_channel       (GimpPlugIn      *plug_in);
-GIOChannel    * _gimp_plug_in_get_write_channel      (GimpPlugIn      *plug_in);
+G_GNUC_INTERNAL GIOChannel    * _gimp_plug_in_get_read_channel       (GimpPlugIn      *plug_in);
+G_GNUC_INTERNAL GIOChannel    * _gimp_plug_in_get_write_channel      (GimpPlugIn      *plug_in);
 
-void            _gimp_plug_in_read_expect_msg        (GimpPlugIn      *plug_in,
-                                                      GimpWireMessage *msg,
-                                                      gint             type);
+G_GNUC_INTERNAL void            _gimp_plug_in_read_expect_msg        (GimpPlugIn      *plug_in,
+                                                                      GimpWireMessage *msg,
+                                                                      gint             type);
 
-gboolean        _gimp_plug_in_set_i18n               (GimpPlugIn      *plug_in,
-                                                      const gchar     *procedure_name,
-                                                      gchar          **gettext_domain,
-                                                      gchar          **catalog_dir);
+G_GNUC_INTERNAL gboolean        _gimp_plug_in_set_i18n               (GimpPlugIn      *plug_in,
+                                                                      const gchar     *procedure_name,
+                                                                      gchar          **gettext_domain,
+                                                                      gchar          **catalog_dir);
 
-GimpProcedure * _gimp_plug_in_create_procedure       (GimpPlugIn      *plug_in,
-                                                      const gchar     *procedure_name);
+G_GNUC_INTERNAL GimpProcedure * _gimp_plug_in_create_procedure       (GimpPlugIn      *plug_in,
+                                                                      const gchar     *procedure_name);
 
-GimpProcedure * _gimp_plug_in_get_procedure          (GimpPlugIn      *plug_in);
+G_GNUC_INTERNAL GimpProcedure * _gimp_plug_in_get_procedure          (GimpPlugIn      *plug_in);
 
-GimpDisplay   * _gimp_plug_in_get_display            (GimpPlugIn      *plug_in,
-                                                      gint32           display_id);
-GimpImage     * _gimp_plug_in_get_image              (GimpPlugIn      *plug_in,
-                                                      gint32           image_id);
-GimpItem      * _gimp_plug_in_get_item               (GimpPlugIn      *plug_in,
-                                                      gint32           item_id);
-GimpResource  * _gimp_plug_in_get_resource           (GimpPlugIn      *plug_in,
-                                                      gint32           resource_id);
+G_GNUC_INTERNAL GimpDisplay   * _gimp_plug_in_get_display            (GimpPlugIn      *plug_in,
+                                                                      gint32           display_id);
+G_GNUC_INTERNAL GimpImage     * _gimp_plug_in_get_image              (GimpPlugIn      *plug_in,
+                                                                      gint32           image_id);
+G_GNUC_INTERNAL GimpItem      * _gimp_plug_in_get_item               (GimpPlugIn      *plug_in,
+                                                                      gint32           item_id);
+G_GNUC_INTERNAL GimpResource  * _gimp_plug_in_get_resource           (GimpPlugIn      *plug_in,
+                                                                      gint32           resource_id);
 
-gboolean        _gimp_plug_in_manage_memory_manually (GimpPlugIn      *plug_in);
+G_GNUC_INTERNAL gboolean        _gimp_plug_in_manage_memory_manually (GimpPlugIn      *plug_in);
 
 
 G_END_DECLS