diff --git a/libgimpbase/gimpmetadata.c b/libgimpbase/gimpmetadata.c
index 8af784c19a..ad4d7b9f45 100644
--- a/libgimpbase/gimpmetadata.c
+++ b/libgimpbase/gimpmetadata.c
@@ -48,6 +48,8 @@ struct _GimpMetadata
 
 struct _GimpMetadataPrivate
 {
+  /* dummy entry to avoid a critical warning due to size 0 */
+  gpointer _gimp_reserved1;
 };
 
 struct _GimpMetadataClass