#define isLEXWARN_on (PL_curcop->cop_warnings != pWARN_STD)
#define isLEXWARN_off (PL_curcop->cop_warnings == pWARN_STD)
#define isWARN_ONCE (PL_dowarn & (G_WARN_ON|G_WARN_ONCE))
-#define isWARN_on(c,x) (IsSet(SvPVX(c), 2*(x)))
-#define isWARNf_on(c,x) (IsSet(SvPVX(c), 2*(x)+1))
+#define isWARN_on(c,x) (IsSet(SvPVX_const(c), 2*(x)))
+#define isWARNf_on(c,x) (IsSet(SvPVX_const(c), 2*(x)+1))
#define ckWARN(x) \
( (isLEXWARN_on && PL_curcop->cop_warnings != pWARN_NONE && \