gtk_application_set_accels_for_action(..., "some.action('number')", ..) limited to 32bit integers

Using an numeric detail parameter for an action

  gtk_application_set_accels_for_action (GTK_APPLICATION (self),
					 "win.rev(-10000)",
                                         (const char *[]){ "Left", NULL });

with an int64 parameter type

  gtk_widget_class_install_action (widget_class, "win.rev", "x", on_ff_rev_activated);

fails due to:

Gtk-WARNING **: 16:18:35.837: Trying to invoke action with target '-10000', but action expects parameter with type 'x'

Using G_GINT64_CONSTANT:

gtk_application_set_accels_for_action (GTK_APPLICATION (self),
					 "win.rev(-10000L)",
                                         (const char *[]){ "Left", NULL });

makes glib's parser fail:

Gtk-CRITICAL **: 16:13:01.481: Error parsing action name: Detailed action name 'win.rev(-10000L)' has invalid format: 9-10:invalid character in number

Using 'i' instead of 'x' works as expected but limits e.g. seeking accuracy when using this to ref/ff in a music player of similar.

Maybe I'm just missing something obvious here (if so I'm happy to cook up an improvement to the docs).