diff --git a/COW.xs b/COW.xs
index 08f389f..6f9985e 100644
--- a/COW.xs
+++ b/COW.xs
@@ -7,6 +7,7 @@
 *
 */
 
+#define PERL_NO_GET_CONTEXT
 #include <EXTERN.h>
 #include <perl.h>
 #include <XSUB.h>
@@ -21,10 +22,17 @@
 /* CowREFCNT is incorrect on Perl < 5.32 */
 #define myCowREFCNT(sv)   ((SvLEN(sv)>0) ? CowREFCNT(sv) : 0)
 
+#ifndef newCONSTSUB_flags
+#  define newCONSTSUB_flags(_hv, _nm, _len, _flg, _sv) newCONSTSUB(_hv, _nm, _sv)
+#endif
+
 MODULE = B__COW       PACKAGE = B::COW
 
 PROTOTYPES: DISABLE
 
+# Converted to newCONSTSUB_flags()
+#if 0
+
 SV*
 can_cow()
 CODE:
@@ -38,6 +46,8 @@ CODE:
 OUTPUT:
      RETVAL
 
+#endif
+
 SV*
 is_cow(sv)
   SV *sv;
@@ -69,6 +79,10 @@ CODE:
 OUTPUT:
      RETVAL
 
+
+# Converted to newCONSTSUB_flags()
+#if 0
+
 SV*
 cowrefcnt_max()
 CODE:
@@ -81,3 +95,25 @@ CODE:
 }
 OUTPUT:
      RETVAL
+
+#endif
+
+BOOT:
+{
+    HV* stash; /* get HV* stash from this XSUB's CV*, faster than gv_stashpvs() */
+    if (CvNAMED(cv)) /* EU::ParseXS's ALIAS:/XSANY overwrites C auto var cv */
+        stash = CvSTASH(cv); /* but this module doesn't use the ALIAS: feature */
+    else {
+        GV* gv = CvGV(cv); /* fn call */
+        stash = GvSTASH(gv);
+    }
+#if !B_CAN_COW
+    newCONSTSUB_flags(  stash, "cowrefcnt_max", sizeof("cowrefcnt_max")-1, 0,
+                        &PL_sv_undef);
+    newCONSTSUB_flags(  stash, "can_cow", sizeof("can_cow")-1, 0, &PL_sv_no);
+#else
+    newCONSTSUB_flags(  stash, "cowrefcnt_max", sizeof("cowrefcnt_max")-1, 0,
+                        newSViv(SV_COW_REFCNT_MAX));
+    newCONSTSUB_flags(  stash, "can_cow", sizeof("can_cow")-1, 0, &PL_sv_yes);
+#endif
+}