I was looking over things a little more, and I *think* I know a better approach to solve the warnings. Once I started looking at things, I realized that in at least some of the cases we have an SPObject* we need to end up with. Conceptually that's a GTK+/Glib object, not a C++ one, so we just need to work in the right paradigm My first thought was something like this for sp-flowtext.cpp: void* rawptr = 0; SPObject* source_obj = 0: ... group->layout.getSourceOfCharacter( it, &rawptr, &span_text_start_iter); source_obj = reinterpret_cast<SPObject*>(rawptr); However, Ralf pointed out that using a reinterpret_cast<> itself triggered that warning. After I had that kicking around in my head for a while, I finally realized what I was missing: SP_OBJECT() We need to force an unknown pointer to be one to an SPObject. However, that's a Glib object, not a base C++ one. And we already have that macro to coerce an arbitrary pointer into a pointer to an SPObject. Plus it does all its magic in C-land, not C++ land. So using it should clear up the warnings, and also is the "proper" GTK+ thing to do. However... since I'm only on gcc 3.3 here, can someone else try this to see if it cleans things up on gcc 4.1.x? Thanks (I'm expecting that at the worst the SP_OBJECT macro will have the warning pop back up. But if it does then we'll have a single point in the codebase to change to fix everything, instead of needing to maintain every place that other function is used) Index: src/sp-flowtext.cpp =================================================================== --- src/sp-flowtext.cpp (revision 12065) +++ src/sp-flowtext.cpp (working copy) @@ -558,21 +558,23 @@ if (set_y) sp_repr_set_svg_double(span_tspan, "y", anchor_point [NR::Y]); - union { SPObject *op; void *vp; } source_obj; + SPObject* source_obj = 0; + void* rawptr = 0; Glib::ustring::iterator span_text_start_iter; - group->layout.getSourceOfCharacter(it, &source_obj.vp, &span_text_start_iter); - gchar *style_text = sp_style_write_difference ((SP_IS_STRING(source_obj.vp) ? source_obj.op->parent : source_obj.op)->style, group->style); + group->layout.getSourceOfCharacter(it, &rawptr, &span_text_start_iter); + source_obj = SP_OBJECT(rawptr); + gchar *style_text = sp_style_write_difference ((SP_IS_STRING(source_obj) ? source_obj->parent : source_obj)->style, group->style); if (style_text && *style_text) { span_tspan->setAttribute("style", style_text); g_free(style_text); } - if (SP_IS_STRING(source_obj.vp)) { - Glib::ustring *string = &SP_STRING(source_obj.vp)- + if (SP_IS_STRING(source_obj)) { + Glib::ustring *string = &SP_STRING(source_obj)->string; union { SPObject *op; void *vp; } span_end_obj; Glib::ustring::iterator span_text_end_iter; group->layout.getSourceOfCharacter(it_span_end, &span_end_obj.vp, &span_text_end_iter); - if (span_end_obj.op != source_obj.op) { + if (span_end_obj.op != source_obj) { if (it_span_end == group->layout.end()) { span_text_end_iter = span_text_start_iter; for (int i = group-