diff -ur hivex-1.2.4.old/ocaml/hivex_c.c hivex-1.2.4/ocaml/hivex_c.c
--- hivex-1.2.4.old/ocaml/hivex_c.c	2010-11-26 18:12:20.000000000 +0000
+++ hivex-1.2.4/ocaml/hivex_c.c	2010-12-16 13:53:09.049192941 +0000
@@ -813,7 +813,7 @@
   Store_field (rv, 0, v);
   v = caml_alloc_string (len);
   memcpy (String_val (v), r, len);
-  caml_modify (&Field (rv, 1), len);
+  caml_modify (&Field (rv, 1), v);
   CAMLreturn (rv);
 }
 
Only in hivex-1.2.4/ocaml: hivex_c.c~