Missing argument in gtk_style_context_get(), fooled by varargs.
size = gtk_size_group_new (GTK_SIZE_GROUP_HORIZONTAL);
context = gtk_widget_get_style_context (calendar);
- gtk_style_context_get (context, GTK_STATE_FLAG_NORMAL, &font_desc, NULL);
+ gtk_style_context_get (context, GTK_STATE_FLAG_NORMAL,
+ GTK_STYLE_PROPERTY_FONT, &font_desc, NULL);
font = pango_font_description_to_string (font_desc);
button = gtk_font_button_new_with_font (font);
g_free (font);