diff --git a/lib/core/src/perl/CPlusPlus.xxs b/lib/core/src/perl/CPlusPlus.xxs
index 90fd8fb..5a676c7 100644
--- a/lib/core/src/perl/CPlusPlus.xxs
+++ b/lib/core/src/perl/CPlusPlus.xxs
@@ -33,8 +33,12 @@ const char* skip_contexts[]={ "/Polymake/Core/CPlusPlus.pm",
 // had to be copied from mg.c
 struct magic_state {
     SV* mgs_sv;
-    U32 mgs_flags;
     I32 mgs_ss_ix;
+    U32 mgs_flags;
+#if PerlVersion < 5220
+    bool mgs_readonly;
+#endif
+    bool mgs_bumped;
 };
 
 inline