diff --git a/libgimp/gimpthumbnailprocedure.h b/libgimp/gimpthumbnailprocedure.h
index 0f72736e56..0ff525ba3b 100644
--- a/libgimp/gimpthumbnailprocedure.h
+++ b/libgimp/gimpthumbnailprocedure.h
@@ -40,6 +40,18 @@ G_BEGIN_DECLS
  * The thumbnail function is run during the lifetime of the GIMP session,
  * each time a plug-in thumbnail procedure is called.
  *
+ * [class@ThumbnailProcedure] are always run non-interactively.
+ *
+ * On success, the returned array must contain:
+ * 1. a [class@Image]: this is the only mandatory return value. It should
+ *    ideally be a simple image whose dimensions are closest to @size and meant
+ *    to be displayed as a small static image.
+ * 2. (optional) the full image's width (not the thumbnail's image's), or 0 if
+ *    unknown.
+ * 3. (optional) the full image's height, or 0 if unknown.
+ * 4. (optional) the [enum@ImageType] of the full image.
+ * 5. (optional) the number of layers in the full image.
+ *
  * Returns: (transfer full): the @procedure's return values.
  *
  * Since: 3.0
diff --git a/plug-ins/common/file-xmc.c b/plug-ins/common/file-xmc.c
index 1e199e33f6..f0dac84247 100644
--- a/plug-ins/common/file-xmc.c
+++ b/plug-ins/common/file-xmc.c
@@ -851,9 +851,9 @@ load_image (GFile   *file,
 static GimpImage *
 load_thumbnail (GFile   *file,
                 gint32   thumb_size,
-                gint32  *thumb_width,
-                gint32  *thumb_height,
-                gint32  *thumb_num_layers,
+                gint32  *img_width,
+                gint32  *img_height,
+                gint32  *num_layers,
                 GError **error)
 {
   /* Return only one frame for thumbnail.
@@ -879,13 +879,13 @@ load_thumbnail (GFile   *file,
   gint           height;
   gint           i;
 
-  g_return_val_if_fail (thumb_width, NULL);
-  g_return_val_if_fail (thumb_height, NULL);
-  g_return_val_if_fail (thumb_num_layers, NULL);
+  g_return_val_if_fail (img_width, NULL);
+  g_return_val_if_fail (img_height, NULL);
+  g_return_val_if_fail (num_layers, NULL);
 
-  *thumb_width      = 0;
-  *thumb_height     = 0;
-  *thumb_num_layers = 0;
+  *img_width  = 0;
+  *img_height = 0;
+  *num_layers = 0;
 
   fp = g_fopen (g_file_peek_path (file), "rb");
 
@@ -937,15 +937,15 @@ load_thumbnail (GFile   *file,
           /* this content is image */
 
           size = READ32 (fp, error)
-          positions[*thumb_num_layers] = READ32 (fp, error)
+          positions[*num_layers] = READ32 (fp, error)
           /* is this image is more preferred than selected before? */
           diff = MAX (thumb_size, size) - MIN (thumb_size, size);
           if (diff < min_diff)
             {/* the image size is closer than current selected image */
               min_diff = diff;
-              sel_num = *thumb_num_layers;
+              sel_num = *num_layers;
             }
-          ++*thumb_num_layers;
+          ++*num_layers;
         }
     }
 
@@ -961,8 +961,8 @@ load_thumbnail (GFile   *file,
   /* get width and height of entire image */
 
   /* Let's make XcursorImages */
-  xcIs = XcursorImagesCreate (*thumb_num_layers);
-  xcIs->nimage = *thumb_num_layers;
+  xcIs = XcursorImagesCreate (*num_layers);
+  xcIs->nimage = *num_layers;
   for (i = 0; i < xcIs->nimage; ++i)
     {
       /* make XcursorImage with no pixel buffer */
@@ -984,13 +984,13 @@ load_thumbnail (GFile   *file,
           thumb_size - min_diff, thumb_size + min_diff);
 
   /* get entire image dimensions */
-  find_hotspots_and_dimensions (xcIs, NULL, NULL, thumb_width, thumb_height);
+  find_hotspots_and_dimensions (xcIs, NULL, NULL, img_width, img_height);
 
   DM_XMC ("width=%i\theight=%i\tnum-layers=%i\n",
-          *thumb_width, *thumb_height, xcIs->nimage);
+          *img_width, *img_height, xcIs->nimage);
 
   /* dimension check */
-  if (*thumb_width > MAX_LOAD_DIMENSION)
+  if (*img_width > MAX_LOAD_DIMENSION)
     {
       g_set_error (error, 0, 0,
                    _("'%s' is too wide for an X cursor."),
@@ -999,7 +999,7 @@ load_thumbnail (GFile   *file,
       return NULL;
     }
 
-  if (*thumb_height > MAX_LOAD_DIMENSION)
+  if (*img_height > MAX_LOAD_DIMENSION)
     {
       g_set_error (error, 0, 0,
                    _("'%s' is too high for an X cursor."),
diff --git a/plug-ins/file-ico/ico-load.c b/plug-ins/file-ico/ico-load.c
index c66cdd2169..dcddeb21cf 100644
--- a/plug-ins/file-ico/ico-load.c
+++ b/plug-ins/file-ico/ico-load.c
@@ -1001,6 +1001,8 @@ ico_load_thumbnail_image (GFile   *file,
   IcoLoadInfo   *info;
   IcoFileHeader  header;
   GimpImage     *image;
+  gint           max_width;
+  gint           max_height;
   gint           w     = 0;
   gint           h     = 0;
   gint           bpp   = 0;
@@ -1042,9 +1044,17 @@ ico_load_thumbnail_image (GFile   *file,
       return NULL;
     }
 
+  max_width  = 0;
+  max_height = 0;
+
   /* Do a quick scan of the icons in the file to find the best match */
   for (i = 0; i < icon_count; i++)
     {
+      if (info[i].width > max_width)
+        max_width = info[i].width;
+      if (info[i].height > max_height)
+        max_height = info[i].height;
+
       if ((info[i].width  > w && w < *width) ||
           (info[i].height > h && h < *height))
         {
@@ -1073,8 +1083,8 @@ ico_load_thumbnail_image (GFile   *file,
                   "Thumbnail", info + match);
   g_free (buf);
 
-  *width  = w;
-  *height = h;
+  *width  = max_width;
+  *height = max_height;
 
   D(("*** thumbnail successfully loaded.\n\n"));
 
diff --git a/plug-ins/file-raw/file-darktable.c b/plug-ins/file-raw/file-darktable.c
index c9cac182b8..f158454608 100644
--- a/plug-ins/file-raw/file-darktable.c
+++ b/plug-ins/file-raw/file-darktable.c
@@ -517,7 +517,7 @@ load_thumbnail_image (GFile   *file,
   gimp_progress_init_printf (_("Opening thumbnail for '%s'"),
                              gimp_file_get_utf8_name (file));
 
-  *width = *height = thumb_size;
+  *width = *height = 0;
 
   if (g_spawn_sync (NULL,
                     argv,