--- CBOR-XS/XS.xs	2013/11/30 17:37:45	1.36
+++ CBOR-XS/XS.xs	2013/11/30 18:13:53	1.37
@@ -99,7 +99,8 @@
 #define F_SHRINK          0x00000001UL
 #define F_ALLOW_UNKNOWN   0x00000002UL
 #define F_ALLOW_SHARING   0x00000004UL
-#define F_PACK_STRINGS    0x00000008UL
+#define F_ALLOW_CYCLES    0x00000008UL
+#define F_PACK_STRINGS    0x00000010UL
 
 #define INIT_SIZE   32 // initial scalar size to be allocated
 
@@ -914,12 +915,22 @@
           if (ecb_expect_false (!dec->shareable))
             dec->shareable = (AV *)sv_2mortal ((SV *)newAV ());
 
-          sv = newSV (0);
-          av_push (dec->shareable, SvREFCNT_inc_NN (sv));
+          if (dec->cbor.flags & F_ALLOW_CYCLES)
+            {
+              sv = newSV (0);
+              av_push (dec->shareable, SvREFCNT_inc_NN (sv));
 
-          SV *osv = decode_sv (dec);
-          sv_setsv (sv, osv);
-          SvREFCNT_dec_NN (osv);
+              SV *osv = decode_sv (dec);
+              sv_setsv (sv, osv);
+              SvREFCNT_dec_NN (osv);
+            }
+          else
+            {
+              av_push (dec->shareable, &PL_sv_undef);
+              int idx = AvFILLp (dec->shareable);
+              sv = decode_sv (dec);
+              av_store (dec->shareable, idx, SvREFCNT_inc_NN (sv));
+            }
         }
         break;
 
@@ -934,6 +945,9 @@
             ERR ("corrupted CBOR data (sharedref index out of bounds)");
 
           sv = SvREFCNT_inc_NN (AvARRAY (dec->shareable)[idx]);
+
+          if (sv == &PL_sv_undef)
+            ERR ("cyclic CBOR data structure found, but allow_cycles is not enabled");
         }
         break;
 
@@ -1209,6 +1223,7 @@
         shrink          = F_SHRINK
         allow_unknown   = F_ALLOW_UNKNOWN
         allow_sharing   = F_ALLOW_SHARING
+        allow_cycles    = F_ALLOW_CYCLES
         pack_strings    = F_PACK_STRINGS
 	PPCODE:
 {
@@ -1225,6 +1240,7 @@
         get_shrink          = F_SHRINK
         get_allow_unknown   = F_ALLOW_UNKNOWN
         get_allow_sharing   = F_ALLOW_SHARING
+        get_allow_cycles    = F_ALLOW_CYCLES
         get_pack_strings    = F_PACK_STRINGS
 	PPCODE:
         XPUSHs (boolSV (self->flags & ix));