diff --git a/glib/gvariant-serialiser.c b/glib/gvariant-serialiser.c
index d5970d2d1..6ebaec7d4 100644
--- a/glib/gvariant-serialiser.c
+++ b/glib/gvariant-serialiser.c
@@ -983,6 +983,10 @@ gvs_tuple_needed_size (GVariantTypeInfo         *type_info,
 
   offset = 0;
 
+  /* We must go through at least one iteration below. If the tuple had no
+   * children, it would have a fixed size. */
+  g_assert (n_children > 0);
+
   for (i = 0; i < n_children; i++)
     {
       guint alignment;