p4raw-id: //depot/perl@24751
#define SvIVX(sv) (0 + ((XPVIV*) SvANY(sv))->xiv_iv)
#define SvUVX(sv) (0 + ((XPVUV*) SvANY(sv))->xuv_uv)
#define SvNVX(sv) (0 + ((XPVNV*) SvANY(sv))->xnv_nv)
-#if PERL_DEBUG_COW > 1
+/* Don't test the core XS code yet. */
+#if defined (PERL_CORE) && PERL_DEBUG_COW > 1
#define SvPVX(sv) (0 + (assert(!SvREADONLY(sv)), (sv)->sv_u.svu_pv))
#else
#define SvPVX(sv) SvPVX_mutable(sv)